Enzyme Regulation
Part I. Introduction
Enzyme Regulation is done in two basic ways:
1. Control of Enzyme Activity Level
A. Noncovalent modifiers cause conformational change between less active and more active states of the enzyme.
B. Covalent Modification causes interconversion between inactive and active forms of the enzyme.
2. Control the Amount of the Enzyme
A. Isozymes - forms of the enzyme which differ in properties but catalyze the same reaction. For example, enzyme forms which differ in Vmax and/or Km. The isozymes can be forms found in different tissues and organs of an animal or for any eukaryotic organism, isozymes can be located in different parts of the cell. For example, different isozymes of lactate dehydrogenase are found in muscle and liver. Malate dehydrogenase occurs in different forms in the cytoplasm and the soluble matrix phase of the mitochondria.
B. Biosynthesis of the enzyme protein can be controlled at the level of the gene via regulation of transcription (ie synthesis of the enzyme's mRNA). This is more of a molecular biologic type of regulation and involves molecules which bind to DNA and influence gene expression. This type of control where the amount of the enzyme is governed can also be done after the mRNA is made, but this is quite rare. In this mechanism, the mRNA is prevented from being translated and since mRNA is rather unstable, it is degraded before it is effectively used by the ribosomes to make the protein.
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©Wilbur H. Campbell, 1995; wcampbel@mtu.edu