The microbiological assay of ‘strepogenin’ with Lactobacillus casei

Abstract

The method was applied to the assay of strepogenin in highly purified proteins. Insulins from various species differed in activity. Liver prepns., as well as some of the pure proteins assayed, seem to contain a factor or factors considerably more potent than the insulin prepn. used as the strepogenin standard. The peptide(s) responsible for the strepogenin activity were shown to be an integral part of the protein molecule and not associated with an impurity such as the hyperglycemic-glycogenolytic factor present in commercial prepns. of crystalline insulins. Glutamine, asparagine and aspartic acid showed a slight strepogenin-like activity; glutamic acid and glutathione were inactive. None of these substances could replace the strepogenin effect of partially hydrolysed proteins.