Carboxypeptidase, pancreatic isolation

A limited amount of information can be obtained by the use of proteolytic enzymes that detach either amino acids or dipeptides sequentially from the C-terminus. They are thus complementary to the aminopeptidases and dipeptidyl aminopeptidases. Two pancreatic enzymes, carboxypeptidases A and B, differ in specificity. The former preferentially liberates C-terminal amino acids with aromatic side chains, somewhat less readily amino acids with alkyl side chains and, more slowly still, other amino acids, but not Pro, Arg, Lys and His. In contrast, carboxypeptidase B releases only C-terminal Arg, Lys and His. Carboxypeptidase Y is much less specific and is capable of removing all amino acids, although Gly and Pro are liberated only slowly. As with aminopeptidases, it is advisable to analyse the hydrolysate at intervals in order to determine the C-terminal sequence of amino acids. An interesting recent development (Carles et al., 1988) uses carboxypeptidase to effect transpeptidation between the protein being sequenced and a tritiated amino acid. The labelled protein is then degraded by various specific methods and then the labelled fragments are isolated by gel electrophoresis and subjected to Edman degradation. 

The carboxypeptidase of pancreatic juice was first isolated in crystalline form by Anson in 1937a. The physical, chemical, and enzymatic properties of this enzyme have been the subject of several recent comprehensive reviews (Neurath and Schwert, 1950 E. L. Smith, 1951a, b, c Green and Neu-rath, 1954) to which the reader is referred. The known physical and chemical properties of the enzyme will be described here. 

Metal Content" of Fractions Attending the Isolation of Carboxypeptidase from Pancreatic Juice... 

Wintersberger2 isolated from bovine pancreatic carboxypeptidase a peptide containing a thiol group involved in the binding of zinc. He first removed the zinc by exposure to a chelating agent (1,10-phenanthroline) or by denaturation, and then labeled the reactive sulfhydryl group by reaction with DDPM and determined the amino acid sequence. 

Supplementing chick diets with a protein fraction, isolated from raw Russet Burbank potato tubers, enriched in proteinase inhibitors, had previously been shown to severely depress their growth (5). The inhibitor-rich fraction contained at least six well characterized inhibitors of mammalian pancreatic digestive proteinases trypsin, chymotrypsin, elastase and carboxypeptidases A and B (5). Since the fraction contained an array of proteinase inhibitors it was not known if CPI contributed to the growth depressing activities. 

---