Phosphoenolpyruvate carboxylase (EC (PEP-C) was purified approximately 770-fold from the mollicute B-PG9. The partially purified PEP-C required phosphoenolpyruvate (PEP) and MnC1 at pH 7·4 or MgC1 at pH 8.6 for optimal activity. The product is oxaloacetate as detected by a malate dehydrogenase indicator system. The (PEP variable) was 0.66 m and the m (bicarbonate variable) was 1.02 m. At low bicarbonate concentrations (0.5 m), PEP-C activity was stimulated approximately 240% by fructose 1,6-bisphosphate. Aspartate was a non-competitive inhibitor of PEP-C activity. The (PEP variable) for aspartate was 0.69 m and the (bicarbonate variable) was 0.99 m. Malate, citrate, isocitrate, 2-oxoglutarate, acetyl-CoA, CMP, CDP, GDP, GTP, ADP and ATP had no effect on the PEP-C reaction. The Hill interaction coefficient was 0.98-1.11. The molecular mass by sucrose density gradient analysis was 353 kDa; by gel filtration chromatography it was 384 kDa. The Stokes radius was about 7.4 nm. PEP-C activity and its inhibition by aspartate in B-PG-9 extracts may reflect an involvement of this enzyme in the interdependent regulation of protein, lipid and nucleic acid precursor metabolism of this TCA-cycle-deficient and cytochrome-less mollicute.


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