Ornithine decarboxylase in bovine corpora lutea

The ornithine decarboxylase (ODC) activity in cytosol and in dispersed cells of bovine corpora lutea was characterized in detail. The enzyme activity was maximal at an assay temperature of 38 C and was linear with respect to both duration of incubation and the amount of cytosol protein or cell number added. The pH optima for the enzyme was rather broad, i.e. 7.2 to 8.5. The apparent Km for ornithine (140-280 micro M) was similar for cytosol and cell ODC. Thiol compounds were required for the maximal enzyme activity and there was an absolute requirement for pyridoxal phosphate as a cofactor, with an apparent Km of 15 micro M. There was a modest competitive inhibition of ODC activity by the end products of ornithine catabolism. Human chorionic gonadotropin (hCG), prostaglandin (PG)E1, PGF2 alpha and cyclic nucleotides had no direct effect on ODC activity. There was no consistent response of ODC in cells and tissues slices pretreated with hCG and PGs. Only the corpus luteum part of bovine ovary of pregnancy contained ODC and this enzyme activity was unchanged throughout pregnancy.