Characterization of a protein factor which causes form interconversion of ornithine decarboxylase in Physarum polycephalum
Augustine, Tom A.
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The first and rate limiting step in polyamine biosynthesis is the conversion of ornithine to putrescine by the enzyme ornithine decarboxylase(E.C. 220.127.116.11). Upon addition of spermidine or spermine to crude homogenates of Physarum polycephalum there was a rapid conversion of the enzyme to its catalytically less active form. This enzyme modification was traced to a heat-labile, trypsin-sensitive, 33,000d protein factor which could be partially purified by DEAE Sephacel chromatography and gel filtration. The conversion reaction was stimulated by spermidine or spermine and was inhibited by NaCl or nucleotide triphosphates in the absence of Mg++. Analysis revealed that the conversion reaction was stoichiometric with respect to the amount of conversion factor added, and was not reversed by gel filtration in high salt even though free conversion factor could be separated from the enzyme. This conversion factor (CF) isolated from Physarum may play a functionally important role in the regulation of polyamine biosynthesis by controlling the levels of physiologically active ornithine decarboxylase.