Kinetic Characteristics, Substrate Specificity and Catalytic Properties of Phosphoserine Aminotransferase from the Green Alga Scenedesmus obliquus, Mutant C-2A

M. Stolz, D. Dörnemann
1995 Zeitschrift für Naturforschung C - A Journal of Biosciences  
Phosphoserine am inotransferase (EC 2.6.1.52) has been purified from Scenedesmus obliquus. mutant C -2A′, as reported previously (Stolz and Dörnemann, 1994). The current studies on its catalytic properties, involving initial reaction velocities as a function of the phosphoserine concentration at various fixed concentrations of 2-oxoglutarate as aminoacceptor, indicate a bi-bi ping pong mechanism . The application of a variety of substrate analogues of phosphoserine revealed no significant
more » ... lisation of these com pounds and thus a considerable specificity of the enzyme. 4,5-dioxovalerate with glutamate as am inodonor is effective as competitive substrate to phosphohydroxypyruvate in the forward reaction and yields 5-am inolevulinate. 4.5-Dioxovalerate and glutam ate-1-semialdehyde can both serve as competitive aminoacceptor in the reverse reaction with phosphoserine and as substrate with 2-oxoglutarate as am inoacceptor. Comparison of the phosphoserine transamination with the transamination of 4,5-dioxovalerate revealed for both reactions a pH -optim um of 6 .8 -7 .0 in Mes/Bis-Trisbuffer. How ever, the Km-values and the Vmax for phosphoserine and 2-oxoglutarate on the one side, and 4,5-dioxovalerate and glutamate on the other were found to differ by orders of magnitude
doi:10.1515/znc-1995-9-1006 fatcat:vrpvziswsbf6tijuuwpyunu36y