CALMODULIN REGULATES NUCLEOTIDE HYDROLYSIS ACTIVITY OF TISSUE TRANSGLUTAMINASE

The interaction of calmodulin with purified guinea pig liver transglut aminase was studied. The nucleotide (ATP and GTP) hydrolysis activity of this tissue transglutaminase was transiently increased and then gra dually decreased depending on calmodulin concentration. The peak activ ation was obtained in the presence of a stoichiometric amount of calmo dulin. The effect of calmodulin on the classical transglutaminase acti vity was minimal. Fluorescence spectroscopy demonstrated that the enzy me produced a significant blue shift in the emission peak of dansylate d calmodulin. Interestingly Ca2+ was not required for the interaction between the two proteins. The results described here give an additiona l regulatory role to calmodulin.