ON THE OPTICAL ROTATION OF I-CYSTINE.

DETERMINATION OF ITS VALUE FOR THE SODIUM AND MER- CURY LINES ANB OF THE TEMPERATURE FACTOR.

BY GERRIT TOENNIES AND THEODORE F. LAVINE.

(From the Research Institute of the Lankenau Hospital, Philadelphia.)

(Received for publication, June 18, 1930.)

The only practical quantitative criterion for the degree of purity of l-cystine is its optical rotation. The importance of a well established and well defined numerical value is obvious in view of the biological and chemical interest attached to this substance.

The present work deals with the purification of Lcystine, by fractionated precipitation, and with rotatory determinations for the Hg and the D lines between 20 and 30”. The literature con- tains no data on the [~y]n~ values of Z-cystine. The [ar], values pre- sented which, as well as the [ol]ng values, were determined under the standard conditions established by Andrews (l), differ substan- tially from his values for the rotation and for the temperature coefficient.

EXPERIMENTAL.

For the purification of crude cystine obtained from hair and wool and previously freed from tyrosine and partly decolorized, use was made of the observations of various authors (2, 3) that the inactive and dextrorotatory modifications are more soluble in water than the l-compound. The material was repeatedly boiled out with large volumes of water adjusted to pH 3 to 4 by means of a few drops of HCI, treated with charcoal in HCI solution, reprecipitated by alkali, and filtered immediately. 20 per cent of the starting material was thus removed; the microscopic examina- tion of the single evaporation residues showed that it consisted largely of fine white needles, in addition to colored impurities present in the first extractions.

153

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154 Optical Rotation of I-Cystine

A sample of the purified cystine was dried to constant weight in presence of PZ06 in DUCUO at 111” and gave the following rotations in 1.02 N HCI. (This acid was used as the solvent in all the follow- ing determinations.)

Iffl& = - 4.894” X 25 cc.

2 X 0.261 gm. = - 234.4”.

[al: = - 4.142” X 25 cc.

2 X 0.261 gm. = - 198.4”.

40 gm. of this material now were extracted four times with water, without pH adjustment, and a fifth time with slightly acid water (pH 3 to 4), 1500 cc. of Hz0 being used each time. About 5 per cent was removed by these extractions, and the last evaporation residues seemed to consist wholly of the hexagonal crystals of I-cystine. The purified cystine was dissolved in 600 cc. of N HCl, precipitated at pH 4 by adding N NaOH and N NaOOCCH3 (total volume of solution 1500 cc.), filtered after standing a short time, and washed with water, alcohol, and ether, yielding 35 gm. of material.

[&g = - 4.7445” X 25.505 gm.

2 X 0.2504 gm. X 1.017 = - 237.59O.

[&- = - 4.077” X 25 cc.

2 X 0.2500 gm. = - 203.85”.

Since on previous attempts, we never succeeded ih increasing the maximum rotation more than 1 or 2 degrees beyond these figures, either by continued extraction with water or by reprecipi- tations with charcoal treatments, a different procedure was chosen to complete the isolation of pure l-cystine; viz., fractionated pre- cipitation at hydrogen ion concentrations outside the isoelec- tric range (4).

3 gm. of the material described above were dissolved in 50 cc. of N HCl (at least 50 per cent more than the stoichiometrically required amount was always found necessary to dissolve the cystine). After filtering and diluting with 300 cc. of HzO, N

NaOH was added until the pH of the solution was about 1.1. Crystallization began immediately; after allowing to stand over- night the precipitate was filtered, and washed with alcohol and ether. By further addition of NaOH to the filtrate (now 500 cc.)

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G. Toennies and T. F. Lavine 155

the pH was brought to 1.6 and the crystallization, which was very slow this time, produced a small volume of heavy, large, hexagonal crystals. They were filtered off and, after removing the filtrate, washed with water, alcohol, and ether as before. The filtrate then was brought to pH 4.7, the crystallized precipitate that formed immediately was filtered off and washed as usual.

A summary of fractionation and optical determinations is as follows :

Fraction I. pH 1.1, 40 per cent yield, 0.2500 gm. cystine in 25.518 gm. solution.

Fraction II. pH 1.6, 27 per cent yield, 0.2510 gm. cystine in 25.4935 gm. solution.

Fraction III. pH 4.7, 24 per cent yield, 0.2502 gm. cystine in 25.5115 gm. solution.

The specific gravities used are based on the determinations re- ported later.

Fraction No.

I II II

III III III

-

_

-

t (average) “C. -‘a Hg (average). -Wk,

29.20 4.801 240.93 29.86 4.801 239.77 29.32 4.826 241 .OO 29.45 4.757 238.48 29.31 4.754 238.31 30.48 4.709 236.14

Since Fractions I and II seemed to show no appreciable differ- ences, a solution of Fraction I was used to study in detail the rela- tion between D and Hg rotations and the influence of temperature (see Tables I and II).

Method of Optical Determinations.

A Landolt precision polarimeter with 0.01” vernier divisions made by Schmidt and Haensch was used. The light source for the D line (5892.5 A) was a Bunsen burner the flame of which was fed by air pressure with a spray of a 20 per cent NaCl solution by means of a glass aspirator and a metal hood attachment on the burner.1 The light from this lamp passed through a 30 mm.

l This arrangement, which is furnished by the Central Scientific Com- pany, Chicago, can be recommended.

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156 Optical Rotation of I-Cystine

layer of 3 per cent K.JI?rZ07 solution inse@ed in the front end of the polariscope. For the Hg line (5461 A) a Lab-Arc Hg lampa with two Corning glass filter plates, “G-555-B.E. didymium, 5.13 mm. thick” and “G-34-y”, was used. The instrument was stand- ardized for the two lines used against a quartz control plate with a Bureau of Standards certiilcate. A half shadow angle of 3-3+” for the D line and of 1%” for the Hg line gave the most accurate read- ings. For each group of determinations a blank of the empty in- strument was determined. For all of the following determina tions (as for some of the preceding ones) a Schmidt and Haensch 200 mm. tube (model No. 83) with water jacket and ground-in thermometer (10-32” in 0.1” divisions) was used. The thermome- ter was checked against a Bureau of Standards standard. After trying various constant temperature devices, an electric rheostat with water circulation3 was found to furnish a simple and suitable arrangement in connection with a constant level water container fed directly from the cold water line. By varying the height of the water container and, if necessary, the rheostat adjustment, any desired temperature could quickly be obtained. When the water jacket of the tube was supplied in this manner the tempera- ture in the tube as a rule did not vary more than O.lM.2” during the time required to take a group of about 10 single readings. At each temperature level a group of at least 8 readings was taken, the temperature being registered each time immediately after the polariscope adjustment. By averaging within each group the recorded temperatures and rotation angles, the figures tabulated below were obtained. They are corrected for a small constant deviation produced by the tube filled with the pure HCI.

The specific gravities were determined at three temperatures for a 25 cc. solution containing 0.250 gm. of cystine in 1.02 N HCl, by comparing the weight of the solution with an equal volume of freshly boiled water. The probable accuracy of these determina- tions is ~tO.0002 corresponding to about f0.04” [LY]. The follow- ing values were found: 1.0190 for 20”, 1.0180 for 25”, and 1.0168 for 30”. By interpolation from these figures the specific gravities corresponding to the experimental temperatures were obtained.

The solution used on both the D and Hg series contained 0.2500

2 Cooper Hewitt Electric Company. s Central Scientific Company.

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G. Toennies and T. F. Lavine 167

gm. of cystine (Fraction I, see above) in 1.02 N HCI, the weight of the solution being 25.518 gm.

The rotatory determinations are given in Tables I and II. By dividing each series into two equal groups (of five and one-

half and six and one-half members, respectively) and developing the equations of the straight lines from the formulze

and

2’~ = Z’a - b Z’X

where ZZ represents the sum of the [cy] values found and Zy the sum of the corresponding temperatures, while Z’ and ~9’ refer to the sums of the first and second halves of the readings, respec- tively, we obtain the two equations

(1) y = 128.18 - 0.48509 z for the D series

and

(2) y = 128.62 - 0.41305 x for the Hg series

or, for the actual specific rotations

(3) [alI) = 2.0615 to - 264.24”

and

(4) r&, = 2.421 to - 311.40”

In Column 5 of Tables I and II, the [a] values calculated from these equations are given and in Column 6 the deviations. From equations (1) and (2), it appears that the intercept on the y axis is practically the same for both series; and this points strongly to the fact that actually both rotations become zero at the same tem- perature. A calculation based on this assumption changes the figures merely to an insignificant extent and agrees with the experimental data just as well. Therefore, and in view of the fact that, as judged from the unusually large temperature factor, the optical rotation of the I-cystine cation presents a case quite out of the ordinary4 we assume that the temperature curves of the D and Hg rotations are straight lines over the range investigated

4 Cf. the interesting review on the determining factors of optical rotation and dispersion by Patterson (5).

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TABLE I.

D Series.

Average temper-

ature.

0)

Specific Specific rotation rotation found. calculated

(4) (5)

-or-l; -T-IS

202.04 201.88 202.77 202.645 202.87 203.115 204.46 204.125 205.70 206.31 210.18 209.71 212.66 212.89 214.40 214.04 217.19 217.67 219.63 219.98 222.36 221.895

AlWag.? rotation.

(2)

Specific gravity.

(3)

t “C. -001

30.25 4.025 1.0167 29.88 4.040 1.0168 29.65 4.042 1.0169 29.16 4.074 1.0170 28.10 4.100 1.0173 26.45 4.191 1.0177 24.91 4.242 1.0180 24.35 4.277 1.0181 22.59 4.334 1.0185 21.47 4.384 1.0187 20.54 4.439 1.0189

Deviation.

(6) -

--

-

+0.16 +0.125

f0.335

+0.47

f0.36

+0.465

-0.245

-0.61

-0.23

-0.48 -0.35

f1.915 $1.915

-1.915

+3.830+ ll= fO.35" -

TABLE II.

Hg Series.

Specific gravity.

(3)

-

_ -

Specific rotation found.

(4)

4 -“bl~,

1.0167 237.65 1.0168 238.64 1.0169 239.06 1.0170 240.59 1.0171 241.27 1.0173 243.23 1.0177 248.13 1.0181 251.59 1.0182 252.79 1.0184 254.94 1.0186 258.08 1.0187 259.38 1.0189 262.85

-

AVXi‘ge rotation.

(2)

Specific rotation

:alculated

(5)

Deviation.

(6) -

-

t “C.

30.50 4.734 30.11 4.754 29.82 4.763 29.39 4.794 28.90 4.808 28.01 4.848 26.17 4.948 24.48 5.019 24.15 5.043 23.18 5.087 21.94 5.151 21.73 5.177 20.32 5.248

+I~, 237.56 238.505 239.205 240.245 241.435 243.58 248.045 252.135 252.935 255.28 258.285 258.795 262.205

+0.09 f0.135

+0.345

+0.085

+0.585 $0.645

-0.145

-0.165 -0.35

-0.545 -0.145 -0.34 -0.205

$1.885 $1.895

-1.895

+3.780+ .3 = drO.29"

158

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G. Toennies and T. F. Lavine 159

and that these straight lines would intersect at [cr], = [ollHg = 0”

in accordance with the following equations.

(5) 2/, = 128.19 - 0.48516 z D

and

(6) YHO = 128.19 - 0.41133 ZHg

or,

(7) [(Y]; = 2,061 t” - 264.23’

and

(8) rff1;, = 2.431 to - 311.65’

By dividing the average error between temperature and polariscope readings Ilt(O.06” - O.O03”or,,) is obtained as the average obser- vation error.

The changes in specific rotation for lo obtained from equations (7) and (8), 2.061” [a], and 2.431” [a],,, were now used for the cor- rection of specific rotations to a common temperature basis. The figures obtained above on Fractions I, II, and III and their start- ing material, thus corrected to 29’ give

Fraction I Fraction II Fraction III Starting

kl& bl& bl2;;, material

bG,

degrees degrees degrees degrees

-241.42 -241.86 -239.57 -238.46 -241.15* -241.78 -239.26

-239.74

Average -241.29 ho.14 -241.82 f0.04 -239.52 f0.18

*From equation (8).

It appears now that the rotation of Fraction II is actually about 0.5” higher than that of Fraction I, while Fraction III rotates 1.8” lower than Fraction I and the best fraction (Fraction II) is about 3.4” above the starting material. The best separation, therefore, seems to take place between the fractions precipitated above and below a pH of about 2.

Consequently, Fractions I and II were combined and treated as follows: 1.55 gm. of cystine were suspended in 250 cc. of HPO and dissolved by addition of 100 cc. of N HCI. To the filtered

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160 Optical Rotation of I-Cystine

TABLE III.

Results of First Rejractionation.

Fraction I A. pH 1.7, 49 per cent yieId. Solution 1. 0.2500 gm. cystine in 25.4635 gm. solution.

‘I 2. 0.1530 “ “ “ 15.801 “ “

Fraction I B. pH 3.9, 39 per cent yield. Solution 1. 0.2508 gm. cystine in 25.457 gm. solution.

“ 2. 0.2501 -‘I “ “ 25.4575 -U ‘I 3. 0.2252 “ “ “ 25.659 “

---- IA 1 29.544.815 242.44

27.284.915 241.82 2 29.494.739 241.83

29.064.768 242.24 26.294.872 242.26 23.575.031 241.92

Avera$e . . . . . . . . -242.08 f0.28’

d .o ‘: E

IB 1 29.3! 27.8( 27.0:

2 29.9: 28.11 27.61 25.5(

3 27.61 28.8: 30.0:

-

_ _

54 14 34 54 %4 k4 14 34 74 14

I‘

“

:.81E :.QOl :.93C :.77E :.86E :.89C :.QQC :.37E :.311 :.26E

7

.-

i

, i i 1 ) i

;

-

241.20 241.57 241.25 241.29 241.44 241.80 241.00 241.75 241.13 241.65

-241.41 zkO.23”

TABLE IV.

Results of Second Rejractionation.

Fraction I AA. pH 1.8, 60 per cent yield. Solution. 0.1218 gm. cystine in 13.7225 gm. solution.

t (average) “C. --‘aHg (average). -+Gg

24.28 4.675 241.74 24.79 4.553 241.69 26.32 4.488 241.89 28.05 4.406 241.65 30.25 4.313 241.97

Average...................................... -241.79 xt0.11”

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G. Toennies and T. F. Lavine 161

solution N NaOH was added until the pH was 1.7. Crystalliza- tion appeared very slowly and was allowed to continue overnight. The precipitate was then filtered, washed with water, and after saving the filtrate, washed with alcohol and ether (Fraction IA). The filtrate (about 500 cc.) was brought to pH 3.9 by addition of N NaOH, the crystals being filtered off the next day and washed and dried as usual (Fraction IB, see Table III).

On comparing the figures given in Table III with the ones ob- tained on Fractions I and II, it is evident that the fractionation obtained is very similar to the preceding one. The reason why in the latter the first fraction had the slightly lower rotation may lie in the fact that the conditions of precipitation caused Fraction I to crystallize rapidly, thereby possibly carrying down traces of inactive cystine, while Fraction II crystallized very slowly and in well defined single hexagons. From these results it appears that, if the maximum rotation is still higher than the value obtained on Fraction I A, the tendency would be disclosed by a partial slow reprecipitation of Fraction I A at a pH lower than 2.

0.20 gm. of Fraction I A were dissolved in 3 cc. of N HCI and diluted with 96 cc. of HzO. By addition of N NaOH, the pH was brought to about 1.8. Crystals began to form slowly; after 24 hours they were filtered, washed, and dried as usual (Fraction IAA, see Table IV).

The results on the various fractions are summarized in the ac- companying diagram.

Starting material 238.46

I 1 I pH 1.1 pH 1.6 pH 4.7

I II III 241.29 241.82 239.52

I I

& pH 1.7 pi 3.8

IA IB 242.08 241.41

I pH 1.8

I AA 241.79

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162 Optical Rotation of Z-Cystine

It appears that no further purification was obtained and that Fractions I, I A, and I AA gave the same rotation within the limits of experimental error.

Comparing the corresponding D figures with the one given by Andrews (1) and being aware of his work on the solubilities of the different optical modifications of cystine (3), we could not yet be satisfied as to the purity of our material. Consequently, a new preparation, starting with our cystine of [a]:g = -238.5”, was made in the manner described by repeated fractionated precipita- tion at different pH values. We thus obtained a sample that gave the following rotations (corrected for 29’).

W Hg = -241.80”, -241.68”, -241.85”; average, -241.78” f 0.06”

This material was used in the following solubility determinations

TABLE V.

Xolubility Determinations.

c~ot~f~~~~~~ in Corresponding to eolution. / gm. in 1000 co.

bs.

127 105

105

gm. gm.

0.05 0.0066 0.0069 0.135 3tO.003 0.05 0.0067 0.0066 0.133 f0.001

2.00 ;:;;;

Glass-stoppered bottles containing 300 cc. of Hz0 and the amounts of cystine given in Table V were shaken on a machine for 4 and 5 days, respectively, at 24-27.5”. In the filtered solutions the amount of dissolved cystine then was determined by evaporat- ing 50 cc. samples on the steam bath to a small volume, placing them in a vacuum desiccator over CaC&, and weighing after the residues were completely dry. The pH of the water used was, determined calorimetrically, 6.3 to 6.4 while the saturated solu- tions showed pH 6.4 to 6.5. The solubility figures obtained are somewhat higher than the minimum solubilities usually given6 but they seem to be in fair agreement with the determinations of Sano (7) about solubility and hydrogen ion concentration. The

5 For review see (3) and (6).

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G. Toennies and T. F. Lavine 163

fact that no difference appears between the amounts dissolved from differently sized samples must, in view of the work of Andrews and De Beer (3), be considered as additional proof for the homo- geneousness of our material.

Taking the grand average of the average determinations ob- tained on four different samples:

-241.79’ ~0.11” (five single determinations) -241.82” f0.01” (two “ “

1 -242.08” rtO.28” (six “ “

-241.78” f0.06” (three “ “ ;

we find [cY]~~ = -241.87” ~0.15’ as the most probable expression for the specific rotation of l-cystine.

The standard value obtained on Fraction I was Icy]; = -241.15’ or 0.72” less than the above value. The corrected equation (8) therefore would be

[or]& = 2.431 to -312.37”

and, herefrom calculated, the corrected equation (6)

yxg = 128.48 -0.41133 zEap,

and the corrected equation (5)

ye = 128.48 -0.48516 ZD

The best expressions for the specific rotation of I-cystine between 20 and 30” in a concentration of 1.0 gm. in 100 cc. of N HCI then are:

[aI& - (2.431 t - 312.37)’ f 0.2’

and

[a]; = (2.061 t - 264.84)’ f 0.2”

DISCUSSION.

In our work we were originally guided by the value -215.5” established by Andrews (1) for the purpose of so standardizing conditions ‘[that values . . . shall accurately indicate . . . the relative concentration of cystine.” We followed the condi- tions established by Andrews for the concentration and encoun-

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164 Optical Rotation of I-Cystine

tered no difficulties. The numerical values, however, obtained under these conditions disagree with his in two respects. First, we obtained for [a]: the value -205.1 f0.2” as compared with -215.5”, and second, for the average temperature coefficient between 20-30” we find -2.06’[ar], for -1” against 1.7”[cr], found by Andrews. Our experimental evidence, regarding the system used in purification and the method applied in the optical determinations, as well as our solubility data and the microscopic appearance of the crystals, indicate that we have been dealing with a practically pure preparation of I-cystine.

For our figures we find some support in the literature. Fischer and Suzuki (8), when establishing the disputed identity of cystine from hair and from cystine stones, found on careful purification “not only from tyrosin but also from racemic cystine:”

[a]; = - 11.84° X 12.2400 gm. 2 X 0.3172 gm. X 1.029

= - 221.9” for hair cystine

and

14: = - 8.70” X 16.7151 gm.

2 X 0.3176 gm. X 1.024 = - 223.6’ for stone cystine

The concentrations are 2.67 gm. and 1.95 gm. of cystine to 100 cc. of 1 N HCl. Both concentrations, especially the latter one, fall within the limits of practically constant rotation as established by Andrews (1). Our value for the same temperature, [cx]~ = -223.6 =tO.2”, is identical with the maximum value of Fischer. Abderhalden (9) obtained under similar conditions [cY]~ = - 223.8” for hair cystine and [(Y]: = -224.4” for stone cystine; figures that are again of the same order as our value. Some further support may be seen in a publication of Morner (10) containing a very large amount of data on the isolation of cystine from a wide variety of protein substances. The highest value reported by Miirner is [a], = -223”; and this value he found consistently on prepara- tions of such different origins as horn, human hair, skin lining of the egg shell, and blood proteins. The concentrations used are all in the neighborhood of 1 per cent in 1 N HCl. As the temper- ature is not reported, room temperature (about 20”) may be assumed. It is difficult to conceive of materials of identical

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G. Toennies and T. F. Lavine 165

rotations resulting from such diverse preparations unless a pure chemical individual was obtained in each case. As regards the temperature factor in the rotation of I-cystine hydrochloride in 1 N

HCl, its large influence appears of special interest when compared with other substances. The earlier authors seem to have over- looked its importance in accurate and comparable determinations; and we find it first mentioned by Andrews (1) who, however, does not indicate whether a plus or a minus sign is to be used for the corrections. Evidently this has given rise to some misinterpreta- tion, to judge from a recent publication by Gortner and Sinclair (11) in which it is stated, referring to a material of [cY]~ = -201.01”, that “Accordingly the preparation can be regarded as practically pure I-cystine.” In truth, this rotation does not indi- cate more than 90 per cent l-cystine.

The fact that our experimental values for D and Hg rotation indicate a straight line relation between rotation and temperature may prove helpful for the future explanation of the steric changes involved.

SUMMARY.

1. By systematic fractionated reprecipitation from acid solu- tion at different hydrogen ion concentrations, a sample of l-cystine is prepared which on further purification showed no further change in optical rotation.

2. The rotation of D and Hg light by a 1 per cent solution of I-cystine in 1 N HCl is determined over the range of 20-30”. Details about the optical method are given. For identification purposes, the Hg light is found more convenient and accurate.

3. The value found for the rotation of I-cystine, while 10” lower than the one recently reported by Andrews (l), is shown to be in agreement with the observations of several of the earlier investigators.

4. Attention is called to the unusually large temperature factor of the optical rotation and to the apparent existence of a straight line relation between temperature and rotation.

BIBLIOGRAPHY.

1. Andrews, J. C., J. Biol. Chem., 66,147 (1925). 2. Miirner, K. A. H., 2. physiol. Chem., 28,595 (1899). Hoffman, W. F.,

and Gortner, R. A., J. Am. Chem. Xoc., 44, 357 (1922). Andrews, J. C., J. Biol. Chem., 74, p. xiii (1927).

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Optical Rotation of I-Cystine

3. Andrews, J. C., and De Beer, E. J., J. Physic. Chem., 32, 1031 (1928). 4. Andrews, J. C., J. Biol. Chem., 74, p. xii (1927). 5. Patterson, T. S., SC. Progress, 17,60 (1922). 6. Brix, G., 2. physiol. Chem., 1’78,109 (1928). 7. Sano, K., Biochem. Z., 168,14 (1926). 8. Fischer, E. and Suzuki, U., 2. physiol. Chem., 46,409 (1905). 9. Abderhalden, E., 2. physiol. Chem., 61, 391 (1907).

10. Morner, K. A. H., 2. physiol. Chem., 34,207 (pp. 208, 309, 310, 318, 321, 334) (1901-02).

11. Gortner, R. A., and Sinclair, W. B., J. Biol. Chem., 83,681 (1929).

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Gerrit Toennies and Theodore F. LavineTEMPERATURE FACTOR

MERCURY LINES AND OF THEVALUE FOR THE SODIUM AND

-CYSTINE : DETERMINATION OF ITSlON THE OPTICAL ROTATION OF

1930, 89:153-166.J. Biol. Chem. 

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CORRECTIONS On page 236, Vol. lxxxvi, No. 1, March, 1930, Fig. 2, Curve I, the point

plotted as pH 4.63 and ordinate 0.7 cc. should be at ordinate 0.8 cc.

On page 162, Vol. b&xix, No. 1, November, 1930, line 2, readFractions IZ, Z A, and I AA for Fractions I, Z A, and Z AA.