Regulation of S-adenosylmethionine decarboxylase during the germination of sporangiospores of Mucor rouxii

Abstract

Summary General properties of S-adenosylmethionine decarboxylase (SAMDC) from Mucor rouxii were studied. Dormant spores of the fungus did not contain detectable levels of the enzyme, but it started to be synthesized at early stages of spore germination. Kinetics of synthesis changed before emergence of the germ tube, with a corresponding increase in a second SAMDC activity which, in contrast to the one originally synthesized, was not activated by putrescine. Development of the second enzyme activity required de novo protein synthesis. Neither enzymic activity was stimulated by Mg2+. Addition of the SAMDC inhibitor methylglyoxal bis-(guanylhydrazone) (MGBG) stopped fungal development in growth phase Ia: cells became spherical and showed ultrastructural alterations. Although MGBG inhibited polyamine formation, it barely inhibited protein and RNA biosynthesis during the first hour of incubation. However, at later periods, biosynthesis of both macromolecules was strongly decreased. When MGBG was added to growth media 3 h after inoculation of spores, it did not affect spore germination and outgrowth. A hypothesis for two different roles of spermidine and putrescine in spore germination is discussed.