Phosphoserine aminotransferase, the second step-catalyzing enzyme for serine biosynthesis

As a step toward analyzing the serine biosynthetic pathway in mammals, me have studied the properties of phosphoserine aminotransferase, the second step-catalyzing enzyme. The K-m values for 3-phosphohydroxypyruvate and L-phosphoserine are 5 and 35 mu M, respectively, and those for glutamate and alpha-ketoglutarate are 1.2 and 0.8 mM, respectively. The product inhibition studies strengthened the support for a ping-pong mechanism and allowed evaluation of K-i values for the four substrates, The equilibrium constant evaluated from the kinetic parameters is similar to 40. Additionally; some physical properties relative to the bound coenzyme and the secondary structure were investigated. The results are consistent with a structural relationship between the Escherichia coli enzyme and the mammalian enzyme. The mammalian enzyme has specific kinetic parameters, the determination of which is a prerequisite to analyzing the serine biosynthetic pathway in mammals.