324 – Carboxypeptidase G3

Publisher Summary This chapter describes the structural chemistry and the biological aspects of carboxypeptidase G3. Carboxypeptidase G3 consists of four subunits of identical molecular mass of 15 kDa. The pI is estimated to be 7.2. The enzyme is suspected to be a zinc-dependent metallopeptidase. The amino acid sequence and gene for carboxypeptidase G3 are not known yet. The enzyme exists on the cell membrane of Pseudomonas sp. bacteria and seems to be a constitutive enzyme. The enzyme shows in vitro antitumor activity. Carboxypeptidase G3 very slightly inhibits the growth of murine leukemia, but shows remarkable antitumor activities against human carcinoma KB and PC-3 cells among ten kinds of human carcinoma cell lines. Its antitumor activity mechanism seems to be based on the degradation of folic acid. Unlike carboxypeptidases G, G1 and G2, the carboxypeptidase G3 acts not only on the L-form of acidic amino acids, but also on the D-form and slightly hydrolyzes Bz-DL-Glu. However, some properties such as C-terminal glutamate-releasing activity and the requirement for Zn2+ are quite similar to those of the other enzymes.