GUANOSINE DEAMINASE AND GUANINE DEAMINASE FROM TEA LEAVES

Guanosine deaminase and guanine deaminase were partially purified from tea leaves. The optimum activity of guanosine deaminase was observed at pH 7.5 and that of guanine deaminase was at pH 7.0-7.5 and 8.5. Gua nosine deaminase was an unstable enzyme. The activities of these deami nases were significantly inhibited by heavy metals. Molecular weights of guanosine deaminase and guanine deaminase as measured by gel filtra tion were about 18,000 and 54,000, respectively. The K-m for the respe ctive substrates, guanosine and guanine, were 9.5 mu M and 41.7 mu M. Guanosine deaminase was considered to catalyze the deamination of 2'-d eoxyguanosine besides guanosine. It is suggested that guanosine deamin ase as well as guanine deaminase in tea leaves not only acts on the ca tabolic pathway, but also is involved in the biosynthesis of caffeine from guanosine or guanine nucleotides.