[Specific proteases which degrade prolactin in the mammary glands; subcellular localization and inhibitory analysis].

The intracellular fractions were shown to contain neutral and acidic proteases hydrolyzing (125I) prolactin with pH optima at pH 7.6 and 3.0. Neutral proteases are predominantly localized in the mitochondrial and nuclear fractions, while the acidic ones--in the lysosomes. Mitochondrial and lysosomal proteases are specific towards rat prolactin. The rate of rat prolactin proteolysis in these fractions is 2.7 (P less than 0.0027) and 1.6 (P less than 0.05) times higher than that of sheep prolactin or that of the luteinizing and follicle-stimulating hormones. Neutral proteases, which split of [125I] insulin, are distributed in the subcellular fractions in quite a different way. It was demonstrated that the prolactin-hydrolyzing activity of the nuclear and mitochondrial fractions is due to the presence of metal-dependent, serine and sulfhydryl proteases in these organelles.