Fragmentation of proteins by S. aureus strain V8 protease. Ammonium bicarbonate strongly inhibits the enzyme but does not improve the selectivity for glutamic acid.

Staphylococcus aureus strain V8 protease is a serine endopeptidase which cleaves peptide bonds at the carboxyl side of Glu and Asp. Specific cleavage at Glu has previously been achieved in ammonium bicarbonate whereas in sodium phosphate cleavage at both Glu and Asp was observed. However, it is shown here that bicarbonate does not restrict the specificity to Glu-X bonds, it simply inhibits the enzyme. The degradation of a mixture of oxidized insulin and glucagon proceeds similarly in the two buffers, although faster in phosphate.