Lecture 20 Enzymes and Vitamins

Enzymes are catalysts. They lower the the activation energy of reaction so that they can take place rapidly at physicological temperatures and generally physicological pH. They are present in very small amounts, they are generally proteins and often contain a metal

Enzymes are generally very specific; they catalyze some specific chemical process; in order to perform their function, they often need specific substances called co-factors. If the body does not produce this material, it must be present in the diet; these cofactors are called vitamins.

Vitamins are classified on the basis of their solubility: fat or water soluble vitamins

Water Soluble Vitamins

Some Water Soluble Vitamins

Fat Soluble Vitamins

The most prevalent form of vitamin D is vitamin D3, or cholecalciferol. Technically, this is not a vitamin, because it is not required in the diet. In skin, vitamin D3 is synthesized from 7-dehydrocholesterol by the ultraviolet rays from sunlight. In regions of limited sunlight, vitamin D3is added to milk products to avoid a vitamin D3deficiency. Its function in the body is to regulate the absorption of phosphorus and calcium during bone growth.

Enzymes may recognize and catalyzea single substratea group of similar substratesa particular type of bond

Isoenzymescatalyze the same reaction in different tissues in the body;lactate dehydrogenase (LDH), which converts lactate to pyruvate, consist of five isoenzymes;they can be used to identify the organ or tissue involved in damage or diseaselactate dehydrogenase have one form more prevalent in heart muscle and another form in skeletal muscle and liver tissue

lactate dehydrogenase (LDH) is an enzyme made up of two polypeptide subunits,

Diagnostic enzymescan determine the amount of damage in tissues;elevated levels may indicate damage or disease in a particular organ;levels of the enzyme creatinekinase (CK), lactic dehydrogenase(LDH), and aspartate transaminase(AST) are elevated following a heart attack are used to determine the severity of the attack

Zymogens (proenzymes) are inactive forms of enzymes;they are activated when one or more peptides are removed

Example: The zymogen proinsulin is converted to its active form, insulin, by removing a small peptide chain

Digestive enzymes are produced as zymogens in one organ and transported to another, such as the pancreas, when needed activated by removing small peptide sections

Why is this necessary?

Effect of temperature on enzyme activity

Effect of pH on enzyme activity

Effect of enzyme concentration on rate Effect of substrate concentration on enzyme activity

If a similar substrate binds to an enzyme but does not cause a reaction, the turnover rate of the enzyme is sharply decreased. This is reversible competitive inhibition and this is how many drugs work.

In irreversible inhibition, the drug forms a covalent bond with the enzyme and removes it from circulation. Many antibiotics work in this fashion.

Penicillin

R groups in penicillin

the transpeptidase in bacteria is used in a step to form a cell wall (carbohydrate)