Carboxypeptidase G3

This chapter describes the structural chemistry and the biological aspects of carboxypeptidase G 3 . Carboxypeptidase G 3 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 G 3 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 G 3 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, G 1 and G 2 , the carboxypeptidase G 3 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 Zn 2+ are quite similar to those of the other enzymes.