Abstract
The hypocalcemic protein purified from bovine parotid gland was modified with chemical reagents or by digestion with carboxypeptidase A, the hypocalcemic activities of the treated samples were assayed, and the effect of treatments was examined statistically. Cleavage of the tryptophanyl and tyrosyl residues in the sample was oxidatively done with N-bromosuccinimide, and tyrosyl residues were acetylated with N-acetylimidazole. In both treatmets, the hypocalcemic activities of the treated samples were somewhat low compared to the controls but the effect of the treatments was not significant. However, both treatments in the presence of urea became effective. Oxidation of methionyl residues of the sample with hydrogen peroxide resulted in the retention of the activity, and the effect of oxidation in the presence of urea was not significant. In the modification of free amino groups, the treatment was ineffective when 51.6% of lysyl free amino groups was blocked with trinitrobenzenesulfonic acid, but the effect appeared when free amino groups were eliminated with nitrous acid. After the reduction of disulfide bonds of the sample with 2-mercaptoethanol, the resulting SH residues were modified with 5, 5'-dithiobis (2-nitrobenzoic acid), and the histidyl residues of the sample were acylated with ethoxyformic anhydride, by which effect of these treatments became significant. The sample was digested with carboxypeptidase A at 25°for 4 hr failed to show effect of the treatment. From these results, tryptophanyl, tyrosyl, free amino, disulfide, and histidyl residues may play a role in appearance of the hypocalcemic activity.
