AI Article Synopsis
- The enzyme from cod fish muscle shows significant activity for both decarboxylation of oxalacetate and pyruvate kinase, indicating they are likely performed by the same protein.
- The decarboxylase activity is much lower (0.90 unit/mg) compared to the pyruvate kinase activity (212 units/mg), suggesting a discrepancy in their functional roles.
- Both activities are regulated by competitive inhibitors and display sigmoidal kinetics, making the decarboxylase reaction a valuable model for examining allosteric mechanisms in the enzyme.
Article Abstract
The enzyme from cod fish muscle that catalyzes the irreversible decarboxylation of oxalacetate and is homogeneous by several criteria contains very significant pyruvate kinase activity. For every unit of decarboxylase activity (0.90 unit/mg) there are 235 units of pyruvate kinase activity (212 units/mg). The inability to separate the two activities by a variety of physical techniques indicates that both are due to a single enzyme protein. Improtantly, the two activities appear to take place at the same or overlapping sites on the enzyme. Phosphoenolpyruvate and 4-ethyloxalacetate are strong linear competitive inhibitors of the decarboxylase activity with respect to oxalacetate having dissociation constants of 3.2 and 10.2 muM, respectively, while 4-ethyloxalacetate is a linear competitive inhibitor of the pyruvate kinase activity with respect to phosphoenolpyruvate, Ki - 13.5 muM. In addition, both activities exhibit sigmoidal kinetics for substrates. The differential influence of effectors on substrate cooperativity for the two reactions indicates that the decarboxylase reaction may be an important tool for studying allosteric mechanisms in this enzyme.
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