Kinetic properties of L-serine dehydratase of the rat liver [Proprieta' cinetiche della L-serina deidratasi di fegato di ratto]

Rat liver L-serine dehydratase (E.C.4.2.1.13) catalyzes the deamination both of L-serine and of L-threonine. These reactions show different rates and, at this moment, the "preferential" substrate of the enzyme is not clear. We have analysed, in various experimental conditions, the behaviour of the deaminase reaction toward the two substrates. From the obtained data, it is evident that at lower pH values L-serine and at higher pH values L-threonine, are the preferred substrates, respectively. A peculiar behaviour is shown by Km values, because they are different by changing the pH in the assay mixtures, and changes are related to the presence of pyridoxal-5'-phosphate in the assay mixtures.