Carboxypeptidase B

I.U.B.: 3.4.17.2
Peptidyl-L-lysine(-L-arginine) hydrolase

Carboxypeptidase B (CPB) catalyzes hydrolysis of the basic amino acids, lysine, arginine, and ornithine from the C-teminal position in polypeptides:

It occurs as a zymogen in the pancreas of most vertebrates. See review by Folk (1971). Ferrell et al. (1975) report on its isolation from starfish. Histidine in the C-terminal position is not acted upon (Folk 1971). The enzyme may function in the further degradation of products of tryptic digestion, for which it is specific, very much as CPA is specific for products of chymotrypsin. CPB also manifests an esterase activity which is related to the metal content of the enzyme (Folk and Gladner 1961: see also Zisapel and Sokolovsky 1975).

Because of its high specificity for C-terminal basic amino acids it has found wide use in end-group analysis for sequence determination.

Characteristics of Carboxypeptidase B from Porcine Pancreas:

Enzymatic Reaction (image will open in a new window)

Molecular weight: 34,300 (Folk et al. 1960).

Composition: The enzyme contains 1 gram atom of zinc per mole; the amino acid composition has been determined (Folk 1971). Studies on binding sites have been reported by Moore and Benoiton (1975), Roholt and Pressman (1975), Zisapel et al. (1973b), Zisapel and Sokolovsky (1972). See also Werber et al. (1975) and Zisapel et al. (1975).

Optimum pH: 9 (Wolff et al. 1962).

Extinction coefficient: = 21.4 (Folk 1971).

Specificity: Porcine CPB shows minimal if any activity toward CPA substrates (Folk 1971). See Zisapel et al. (1973a) and Sokolovsky and Zisapel (1971), also Seely and Benoiton (1969) and Jones and Miller (1968).

Inhibitors: CPB is competitively inhibited by arginine, lysine, and ornithine. See Wolff et al. (1962) for kinetic parameters. The enzyme is not inhibited by diisopropylfluorophosphate (DFP) or phenylmethylsulfonyl flouride (PMSF) but is inhibited by metal chelating agents like 1,10-phenanthroline.

Stability: The enzyme is stable for 6-12 months when stored at -20°C.

Related Products:  Carboxypeptidase Y (COY)
Chymotrypsin, TLCK-treated (CDTLCK)
Clostripain, Endo-Arg-C (CP)
Protease, Stap, Endo-Glu-C (STAP) Trypsin, SeqENZ (TRSEQII) & Modified (TRSEQZ)