Abstract
Abstract Phosphoenolpyruvate carboxylase of Escherichia coli was purified to homogeneity. The molecular weight of the native protein, as determined by sedimentation equilibrium analyses, is 402,000. Sedimentation equilibrium analyses on the enzyme denatured in 3.5 m, 5 m, and 7 m guanidine hydrochloride gave a single species with a molecular weight of 99,590. Electrophoretic analyses of the enzyme in polyacrylamide gels in sodium dodecyl sulfate also gave a single species with a molecular weight of 107,000. These data indicate that the carboxylase is composed of four identical subunits, each having a molecular weight of approximately 100,000. Amino acid analyses indicate the presence of 36 cysteine residues per mole, all of which appear to exist as free sulfhydryl groups. The enzyme does not appear to be a metalloprotein. The partial specific volume is 0.737, the sedimentation coefficient is 12.3, and the specific reaction rate is 3.77 x 104 moles of substrate carboxylated per min per mole of enzyme. The diffusion coefficient and the frictional coefficient (f/f0) calculated from the molecular weight, V, and S gave values of 2.84 x 10-7 cm2 sec-1 and 1.53, respectively.
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