Polyamine synthesis in the regenerating rat liver: Stimulation of S-adenosylmethionine decarboxylase, and spermidine and spermine synthases after partial hepatectomy

Abstract

The activities of the enzymes involved in the synthesis of spermidine and spermine, i.e. putrescine-activated S-adenosylmethionine decarboxylase, and spermidine and spermine synthases, increased in rat liver after partial hepatectomy. At early stages of regeneration all these three enzyme activities increased fairly parallelly and were above the control level as early as 12 h after the operation. The activity of S-adenosylmethionine decarboxylase reached a peak, about three times the control level, approx. at 48 h postoperatively and then declined fairly rapidly. Spermine synthase activity showed a time pattern roughly comparable to that of S-adenosylmethionine decarboxylase. Spermidine synthase activity increased up to 96 h and was still elevated at 8 days after the operation. The stimulation of ornithine decarboxylase activity (EC 4.1.1.17) preceded the increases in the spermidine and spermine synthesizing enzyme activities. When cycloheximide was given to partially hepatectomized animals the activity of liver S-adenosylmethionine decarboxylase declined very rapidly with an apparent half-life of about 35 min, whereas no change was observed in the activities of spermidine and spermine synthases within 2 h after the inhibitor. These results are in accord with the view that at least three different proteins are required for the synthesis of spermidine and spermine.