Physarum flavicomum malate dehydrogenase isozymes : The physical, chemical, and kinetic analyses of mitochondrial and supernatant forms

Abstract

The structure and function of malate dehydrogenase isozymes isolated from Physarum flavicomum have been investigated. Two proteins, one localized in the cytosol and one in the mitochondria, demonstrated malate dehydrogenase activity. These proteins were purified by a combination of acetone fractionation, chromatography, and isoelectric focusing. Total purity was defined by electrophoretic, hydrodynamic, and conformational properties. Biochemical and biophysical characteristics established for both isozymes include sedimentation coefficients, molecular weight, subunit molecular weight, isoelectric point, total amino acid contents, and thermal stability. Both isozymes exhibited similar functional properties in regard to optimum pH, optimum substrate concentration, Michaelis constants, and response to certain substrate analogs. The effects of nucleoside phosphates were tested, also revealing a sensitivity of the mitochondrial form to adenosine phosphates, while the supernatant form was relatively unaffected. The extensive analyses offered here are compared with data on malate dehydrogenase isozymes from vertebral sources. The data suggest a strong conservation of the functional properties for these isozymes.