Clin Enzyme

Clinical Enzymology 431 Prof. Fahad J. Al-Shammary Introduction to Enzymes

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Summary The General Characteristics of Enzymes. Enzymes are highly efficient protein catalysts which are involved iii almost every biological reaction. They are often quite specific in terms of the substance acted upon and the type of reaction catalyzed. Enzyme Nomenclature and Classification. Enzymes are grouped into six major classes on the basis of the type of reaction catalyzed. Common names for enzymes often end in -ase and are based on the substrate and/or the type of reaction catalyzed. Enzyme Cofactors. Cofactors are nonprotein molecules required for an enzyme to be active. Cofactors are either organic (coenzymes) or inorganic ions. Mechanism of Enzyme Action. The behavior of enzymes is explained by a theory in which the formation of an enzyme-substrate complex is assumed to occur. The specificity of enzymes is explained by the lock and key theory and the induced fit theory. Enzyme Activity. The catalytic ability of enzymes is described by turnover number and enzyme international units. Experiments that measure enzyme activity are referred to as enzyme assays. Factors Affecting Enzyme Activity. The catalytic activity of enzymes is influenced by numerous factors. The most important are substrate concentration, enzyme concentration, temperature, and pH. Enzyme Inhibition. Chemical substances called inhibitors decrease the rates of enzyme catalyzed reactions. irreversible inhibitors render enzymes permanently inactive and include several very toxic substances such as the cyanide ion and heavy metal ions. Reversible inhibitors are of two types: competitive and noncompetitive. Regulation of Enzyme Activity. Three mechanisms of cellular control over enzyme activity exist. One method involves the synthesis of enzyme precursors called zymogens, which are activated when needed by the cell. The second mechanism relies upon the binding of small molecules (modulators), which increase or decrease enzyme activity. Genetic control of enzyme synthesis, the third method, regulates the amount of enzyme available. Medical Applications of Enzymes. Numerous enzymes have become useful as aids in diagnostic medicine. The presence of specific enzymes in body fluids such as blood has been related to certain pathological conditions.

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Practice Examination 1. An enzyme is known to move an amine group from one material to another. It would be referred to as a(n): j k l m n

lyase

j k l m n

oxioreductase

j k l m n

transferase

j k l m n

hydrolase

j k l m n

movase

2. A catalytically inactive protein formed by removal of the cofactor from an active enzyme is called a(n): j k l m n

activator

j k l m n

apoenzyme

j k l m n

proenzyme

j k l m n

preenzyme

3. The inactive precursor of an enzyme is called a(n): j k l m n

activator

j k l m n

apoenzyme

j k l m n

proenzyme

j k l m n

preenzyme

4. A measure of how many subtrate molecules can be acted on by an enzyme molecule is called: j k l m n

heat of reaction

j k l m n

turnover rate

j k l m n

catalytic speed

j k l m n

activation energy

5. Which would you expect to have an effect on activity of an enzyme. j k l m n

substrate concentration

j k l m n

pH

j k l m n

temperature 32

j k l m n

enzyme concentration

j k l m n

all of the above

6. A zymogen is classified as an inactive form of an enzyme. j k l m n

True

j k l m n

False

7. Which enzyme is useful for detecting pancreatic disorders? j k l m n

amylase

j k l m n

alkaline phosphatase

j k l m n

creatine kinase

j k l m n

lysozyme

8. The enzymatic model that assumes that enzymes have flexable conformations is called: j k l m n

lock and key

j k l m n

induced fit

j k l m n

active site modification

j k l m n

noncompetitive inhibition

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