Physical parameters and possible regulation of zeta-aminolevulinic acid synthetase

Physical measurements were made on the zeta-aminolevulinic acid synthetase from Rhodopseudomonas spheroides. These include a Stokes radius of 3.8 nm, determined by gel filtration, and sedimentation coefficient of 5.46 S by sucrose density gradient centrifugation. From these measurements and the value of partial specific volume of 0.732 ml/g determined from the amino acid composition, the following physical constants were calculated: molecular weight, 88000; diffusion coefficient, 5.65 X 10(-7) cm2s-1; frictional ratio, 1.30; axial ratio, 5.0. The enzyme is inhibited by more than 50% by glyceraldehyde 3-phosphate (1mM), pyruvate (0.02 M), alpha-ketoglutarate (0.02 M), urea (0.8 M), CoCl2 (0.2 mM) and hemin (5 micrograms). The effect of these inhibitors on the possible regulation of this enzymic activity is discussed.