Trichomonas gallinae: charaterization and regulatory properties of lactic dehydrogenase. |
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Authors: | H Betterton C Almond H Dowda |
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Affiliation: | Department of Microbiology and Immunology, University of Arkansas Medical Center, Little Rock, Arkansas 72201, U.S.A.;Baptist Medical Center, Little Rock, Arkansas 72201, U.S.A. |
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Abstract: | The lactic dehydrogenase (l-lactate: NAD oxidoreductase, EC 1.1.1.27, LDH)of Trichomonas gallinae was characterized and some of its regulatory properties studied. Electrophoretic analysis, with specific enzymatic staining of crude and dialyzed cell-free extracts and dialyzed ammonium sulfate fractions, all revealed a single band of enzymatic activity suggesting only one molecular form of the enzyme. The pH optima were found to be the following: 7.0 in the pyruvate to lactate direction and 9.0 in the reverse direction. Thermal inactivation studies showed a narrow temperature optimum peaking at 35 C. The Km values for all four reaction components were determined and found to be: NADH, 70 μm; pyruvate, 88 μm; NAD, 65 μm; and l-lactate, 4.6 mM. T. gallinae LDH was absolutely specific for NAD, NADH, l-lactate, and pyruvate. The enzyme exhibited negative cooperativity, with both NADH and l-lactate, as evidenced by curvilinear Lineweaver-Burk kinetics and Hill coefficients of less than one. Several glycolytic intermediates lowered the Km of NADH with variable effects on the Km of pyruvate. The regulation of LDH by glycolytic intermediates is discussed. |
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Keywords: | Dehydrogenase, lactic (EC 1.1.1.27) EC 1.1.1.27 Enzyme Enzyme regulation Metabolism pH optima Temperature optimum |
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