The Chemical Structure and Enzymatic Functions of Bovine Procarboxypeptidase A

Abstract

Procarboxypeptidase A is the zymogen of an exopeptidase, carboxypeptidase A, which liberates from peptides and proteins carboxyl-terminal amino acids whose side chains conform to the specificity requirements of this enzyme.1 The active enzyme can be isolated from activated bovine pancreatic juice or from drippings of fresh pancreas glands by a procedure originally described by Anson ;2 alternatively, the enzyme can be isolated from acetone powder of unactivated beef pancreas glands by the procedure of Allan,3 which is now undergoing further modifications and refinements. Carboxypeptidase A is a metalloenzyme which is inhibited by 1,10 phenanthroline and other metal chelating agents, zinc being the metal which is functionally and structurally intrinsic to the native enzymes. 4 5 Several molecular parameters pertaining to size, charge properties, and amino acid composition of the enzyme are well established, ' but the detailed chemical structure of this enzyme remains to be elucidated. Experiments to this end are part of a group program now in progress in this laboratory and in the laboratories of B. L. Vallee, Harvard Medical School. Procarboxypeptidase A, the inactive precursor of this enzyme, can be found as such in bovine pancreatic juice, in zymogen granules,6 and in other subcellular components of the acinar cells of the bovine pancreas, and the metabolic origin

Chymotrypsin C mutations in chronic pancreatitis

“…In the pancreatic juice of ruminants, chymotrypsinogen C is found in ternary complex with procarboxypeptidase A (proCPA) and proproteinase E, or in binary complex with proCPA. [41][42][43] The crystal structure of the ternary complex has been determined. 43 The substrate specificity of the activated and chemically dissociated active bovine CTRC was similar to its porcine ortholog.…”

The three-dimensional structure of the native ternary complex of bovine pancreatic procarboxypeptidase A with proproteinase E and chymotrypsinogen C.

“…Proenzymes from the exocrine pancreas constitute useful models for proteolytic processing and enzyme regulation (Neurath, 1989) and many of them have been characterized in depth at both the structural and functional levels (trypsinogen, chymotrypsinogen A, procarboxypeptidases A and B, etc.). Exceptions are chymotrypsinogen C and proproteinase E, which are associated with procarboxypep-tidase A in a ternary complex in ruminants (Brown et al, 1961;Puigserver et al, 1986, Aviles et al, 1993. Conformational studies of the isolated subunits or of the whole ternary complex have been limited in the past because of the strong association between subunits in the complex, because of its large size (100 kDa) and because of its resistance to crystallization, a fact probably related to the rapid autolysis of the proproteinase E subunit (Pascual et al, 1990).…”

“…Ruminant BPE can autolyse during certain isolation procedures, giving rise to the above mentioned N-terminal truncated form, called subunit III, which lacks the first two residues of the mature enzyme (Pascual et al, 1990) and shows a strongly diminished activity (Wicker and Puigserver, 1981). This subunit has been assumed for many years to be an original component of the ruminant ternary complexes (Brown et al, 1961;Kerfelec et al, 1986); now it seems clear, however, that it is an isolation artefact (Pascual et al, 1990;Aviles et al, 1993). The three-dimensional structure of the monomeric subunit III from the bovine digestive system has recently been solved (Pignol et al, 1994) and was considered to be a homology model for the proteinase E zymogens.…”

Crystal structure of an oligomer of proteolytic zymogens: detailed conformational analysis of the bovine ternary complex and implications for their activation 1 1Edited by I. A. Wilson

“…In contrast, PCPA2 and PCPB have been described only as monomers (Pascual et al, 1990;Avile Âs et al, 1993;Oppezzo et al, 1994). Oligomeric PCPA has been found in a binary complex with the serine proteinase zymogens chymotrypsinogens B and C or with proproteinase E in human, pig, whale and rat (for a review, see Avile Âs et al, 1993) or in a ternary complex with the latter two proenzymes in bovine, sheep, camel and goat (Brown et al, 1961(Brown et al, , 1963Kerfelec et al, 1985). The occurrence of PCPA in oligomeric complexes is therefore quite widespread.…”

“…Some clari®cation may be achieved by studies of the ternary complex (TC) of bovine procarboxypeptidase A (bPCPA), chymotrypsinogen C (bCTGC) and proproteinase E (bPPE), a form that can be isolated either from bovine pancreas or pancreatic juice (Brown et al, 1961;Kobayashi et al, 1981a,b;Pascual et al, 1990). This complex was initially termed procarboxypeptidase A-S6, because this proenzyme is the major and ®rst identi®ed component of the complex and because it has a sedimentation coef®cient of 6 S (Brown et al, 1963).…”