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High-Yield Terms
Simple enzyme: binds only substrate and/or inhibitors
Holoenzyme: complex enzymes which are composed of protein plus a relatively small organic molecule
Apoenzyme: the protein component of a complex enzyme
Coenzymes: nonprotein components of enzymes
Isozyme: member of a set of enzymes sharing similar/same substrate specificity
Metalloenzyme: enzymes that require a metal in their composition
Ribozymes: RNA molecules that exhibit catalytic activity in the absence of any protein component
Reaction rate: described by the number of molecules of reactant(s) that are converted into product(s) in a specified time period
Chemical reaction order: relates to the number of molecules in a reaction complex that can proceed to product
Equilibrium constant: related to the ratio of product concentration to reactant concentration or rate constants for forward and reverse reactions
Michaelis-Menten constant (Km): relates the maximum reaction velocity to substrate concentration such that Km is the substrate concentration [S] at which a reaction has attained half the maximal velocity
Lineweaver-Burk plots: linear double reciprocal plots of substrate concentration versus reaction velocity
Allosteric enzymes: defined as any enzyme whose activity is altered by binding small molecule regulators referred to as effectors; plots of substrate concentration versus reaction velocity are sigmoidal instead of curvilinear
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Enzymes are biological catalysts responsible for supporting almost all of the chemical reactions that maintain animal homeostasis. Because of their role in maintaining life processes, the assay and pharmacological regulation of enzymes have become key elements in clinical diagnosis and therapeutics. The macromolecular components of almost all enzymes are composed of protein, except for a class of RNA-modifying catalysts known as ribozymes. Ribozymes are molecules of ribonucleic acid that catalyze reactions on the phosphodiester bond of other RNAs (see Chapter 35) (Table 9-1).
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Enzyme Classifications
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Enzymes are also classified on the basis of their composition. Enzymes composed wholly of protein are known as simple enzymes in contrast to complex enzymes, which are composed of protein plus a relatively small organic molecule. Complex enzymes are also known as ...