Enzyme activity factors that affect

Factors that affect enzyme activity, that is, the rates of enzyme-catalyzed reactions, include ... 

Factors that affect drug metabolism will influence the development of serious adverse effects. TPMT, one of the three enzymes that metabolize 6-MP, is encoded by a gene on chromosome 6 that contains functional polymorphisms. Multiple variants have been described ( 2, 3A, 3B, 3C, 3D, 4, 5, 6, 7, 10 31,32) that result in lower TPMT activity, leading to preferential metabolism of 6-MP by the HGPRT enzyme. This results in an increase in the amount of cytotoxic thioguanine nucleotides and greater myelotoxicity. There appears to be an allele dose-dependent... 

The three coefficients C, e, and R are related in a simple way the responsiveness (R) of a pathway to an outside factor that affects a certain enzyme is a function of (1) how sensitive the pathway is to changes in the activity of that enzyme (the control coefficient, C) and (2) how sensitive that specific enzyme is to changes in the outside factor (the elasticity, e) ... 

Regulatory enzyme. An enzyme in which the active site is subject to regulation by factors other than the enzyme substrate. The enzyme frequently contains a nonoverlapping site for binding the regulatory factor that affects the activity of the active site. 

Enzyme kinetics is studied for two reasons (1) it is a practical concern to determine the activity of the enzyme under different conditions (2) frequently the analysis of enzyme kinetics gives information about the mechanism of enzyme action. Chapter 7, Enzyme Kinetics, begins with an introductory section on the discovery of enzymes, basic enzyme terminology and a description of the six main classes of enzymes and the reactions they catalyze. The remainder of the chapter deals with basic aspects of chemical kinetics, enzyme-catalyzed reactions and various factors that affect the kinetics. 

Factors that affect the rate of enzyme-catalyzed reactions include enzyme and substrate concentration, pH, temperature, and the presence of inhibitors, activators, co-enzymes, and prosthetic groups. 

In practice, the choice of substrate concentrations is limited by such considerations as the solubility of the substrates, the viscosity and high initial absorbance of concentrated solutions, and the relative costs of the reagents. Furthermore, the selection of appropriate substrate concentrations is only one of the factors to be considered in formulating an optimal assay system for the measurement of a specific enzyme activity. Critical choices must also be made with respect to other, frequently interdependent factors that affect reaction rate, such as the concentrations of activators and the nature and pH of the buffer system. The traditional empirical approach to optimization has been replaced by newer techniques of simplex co-optimization and response-... 

To measure enzyme activity reliably, all the factors that affect the reaction rate-other than tlie concentration of active enzyme—must be optimized and rigidly controlled. Furthermore, because the reaction velocity is at or near its maximum under optimal conditions, a larger analytical signal is obtained that can be more accurately and precisely measured than a smaller signal obtained under suboptimal conditions. Much effort has therefore been devoted to determining optimal conditions for measuring the activities of enzymes of clinical importance. 

Some of the most important factors that affect enzyme activity are ... 

Acetyl CoA is converted to malonyl CoA and into fatty acids as described previously. The enzyme that carries out the first committed step for fatty-acid synthesis, acetyl CoA carboxylase, is finely controlled both allosterically and covalently. This enzyme can occur in a monomeric inactive form or a polymeric active form. One factor that affects this is citrate, which stimulates the polymeric or active form of acetyl CoA carboxylase. Thus, citrate plays an important role in lipogenesis as (1) a source of cytosolic acetyl CoA, (2) an allosteric positive effector of acetyl CoA carboxylase, and (3) a provider of oxaloacetate in the cytosol, which can allow transhydrogenation from NADH to NADPH. An allosteric inhibitor of acetyl CoA carboxylase that causes dissociation to the monomeric form is fatty-acyl CoA. Thus, if exogenous fatty acids are available, there is little reason to synthesize more fatty acids. Fatty-acyl CoA in the cytosol decreases malonyl CoA formation by inhibiting acetyl CoA carboxylase. 

List the factors that affect enzyme activity. 

Identify the factors that affect enzyme activity. (Section 10.6) Compare the mechanisms of competitive and noncompetitive enzyme inhibition. (Section 10.7) Describe the three methods of cellular control over enzyme activity. (Section 10.8)... 

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