The reduced nicotinamide adenine dinucleotide-activated phosphoenolpyruvate carboxylase from Pseudomonas MA. Correlation of allosteric properties with changes in the sedimentation behavior.

Phosphoenolpyruvate carboxylase from Pseudomonas MA, grown on methylamine as a sole carbon source, has been studied with respect to some of its regulatory properties. The enzyme shows both negative and positive cooperativity with respect to the substrate phosphoenolpyruvate (Hill coefficients of 0.5 and 1.75). The enzyme requires a divalent cation for activity. Either magnesium or manganous ion is effective. While magnesium shows normal kinetics, manganous ion shows positive cooperativity with a Hill coefficient of 1.4. The enzyme is activated 50-fold by 0.2 mM NADH at 1 mM phosphoenolpyruvate. This activation is hysteretic, showing a lag of 2 to 3 min. Both NADH and Mn2+ induce a change in the sedimentation coefficient of the enzyme from 12.4 to 8.5 as measured by sucrose density gradient centrifugation. High concentrations of phosphate or sulfate are capable of producing this effect on sedimentation, but neither will activate more than 3-fold. Thus, if NADH is an indicator of the total energy level of the cell, the enzyme appears to be susceptible to control by factors which reflect this total energy level. The importance of this control with respect to hypothetical pathways of carbon utilization in the organism is discussed.