CHEMICAL MODIFICATIONS OF AMINO GROUPS OF TRYPSIN

Reactivity of amino groups of chromatographically homogenious β-trypsin was studied by chemical modification. Guanidination by 1-amidinyl-3, 5-dimethyl pyrazole nitrate led to modification of 10 out of 14 lysyl residues per molecule of trypsin. The guanidinating reagent was found to be a competitive inhibitor of trypsin. Extent of acetamidination by methyl acetimidate hydrochloride was affected by pH, temperature and the presence of various competitive inhibitors. All 14 ε{lunate}-amino groups of lysyl residues could be acetamidinated in the presence of the competitive inhibitors at pH 9.5 and 25° without loss of enzyme activity. When 11 or more lysyl residues are modified by acetamidination, the enzyme is stable against autolysis in the absence of Ca++. The enzyme with 10 of its 14 lysyl residues guanidinated loses its enzyme activity by autolysis at neutral pH at a rate comparable with unmodified enzyme. © 1969.