Abstract
Milk-clotting and blood-coagulating activities were determined using various proteinase preparations, mainly of microorganism origin, the substrate specificity of which on the oxidized insulin B chain was known. None of the proteinases which possessed hardly any milk-clotting activity attacked the peptide bond containing phenylalanine at the C-terminal end of insulin B chain. On the other hand, some proteinases which possessed the ability to attack the peptide bond containing phenylalanine at the C-terminal end of insulin B chain did show a high order of milk-clotting activity, but others showing the same substrate specificity on insulin B chain did show hardly any milk-clotting activity. Blood coagulation was not observed with the other proteinases except thrombin and trypsin. The latter two proteinases possessed the activity to split the peptide bond containing lysine at the C-terminal end of insulin B chain. However, the other proteinases which were found to attack not only the C-terminal peptide bond containing lysine but also the other peptide bonds of insulin B chain did not show any thrombinlike activity. From the results obtained in this experiment, it was concluded that either milk-clotting or bloodcoagulating activities of various proteinases were not always correlated with their substrate specificities on the insulin B chain.
