Evidence for the presence of two forms of L-serine dehydratase in rat liver

Abstract

Lserine dehydrates (L-serine hydrolyase (deaminating), EC 4.2.1.13) has been highly purified from rat liver after inducing the enzyme either by feeding the animals with a high-protein diet [l-4] or by fasting them under simultaneous administration of cortisone [4], As reported by Schmidinger and Kroger [5] L-serine dehydratase activity rapidly decreases in rat liver if the animals are fed with a protein-free diet. However, the enzyme level does not reach zero, even after giving the diet for 7 days. The enzyme activity increases again, as soon as the rats are fasted or put on a diet of casein hydrolysate. The present paper deals with the demonstration of two forms of L-serine dehydratase from rat liver. The enzymes are different from each other concerning their molecular weight and heat stability. Five female rats (Sprague-Dawley strain; Ivanovas, Kisslegg/Allglu; weighing 1 lo-130 g) were put on a protein-free diet (protein content less than 1%) for 7 days and thereafter starved for 38 hr in order to get induction of the enzyme. The animals were then killed and their livers removed. These were homogenized (Ultra-Turrax) for 40 set in 4 volumes of 0.14 M KC1 containing 10” M EDTA and 1 OW5 M PALP. The homogenates were centrifuged (105,000 X g; 40 min) and the supernatants were combined. This crude extract is defined as the “induced” enzyme preparation. If the rats, on the other hand, were not starved after getting the protein-free diet for 7 days thus no induction took place the supernatants mentioned above result in an extract called the “non-induced” enzyme preparation. The assay for L-serine dehydratase was carried out according to Schmidinger and Kroger [5], except for the incubation period which