Measurement of the amount of ornithine decarboxylase in Saccharomyces cerevisiae and Saccharomyces uvarum by using α-[5-¹⁴C]difluoromethylornithine

Ornithine decarboxylase (EC 4.1.1.17) activity was about 3-times higher in Saccharomyces uvarum than in Saccharomyces cerevisiae in the middle of logarithmic growth. The enzyme from both sources was inactivated by α-difluoromethylornithine. When the binding of [5-¹⁴C]difluoromethylornithine to yeast ornithine decarboxylase was studied it was shown that S. uvarum extracts contained about 40 ng of active ornithine decarboxylase per mg of cellular protein, and that of S. cerevisiae 10-12 ng of active enzyme. It appeared that S. uvarum ornithine decarboxylase could be highly purified by affinity chromatography, but S. cerevisiae enzyme did not bind to the same column. The purified preparation from S. uvarum had an M_r of 73 000 and a 100-fold purification (purified by conventional methods) of ornithine decarboxylase from S. cerevisiae had an M_r of 69 000 on a gel filtration column. When the purified S. ovarum ornithine decarboxylase was labelled with difluoromethylornithine, it co-eluted with native enzyme on a gel filtration column and it ran as a single band on polyacrylamide gel electrophoresis under denaturing conditions at a position corresponding to an M_r of 72 000, indicating that the active enzyme is a monomer. The loss of ornithine decarboxylase activity after addition of cycloheximide and spermidine to culture correlated with the decrease of the binding of difluoromethylornithine to protein.