Carboxy peptidase

Figure 4.20 Detailed view of the zinc environment in carboxy-peptidase. The active-site zinc atom is bound to His 69 and Glu 72, which are part of the loop region outside P strand 2. In addition, His 196, which is the last residue of P strand 5, also binds the zinc.

While the N-acetyl group likely protects the N-terminus from the action of ami-nopeptidases and the carboxamide moiety protects the C-terminus from carboxy-peptidases, these features alone do not prevent degradation of the control peptide. 

Juillerat-Jeanneret L, Aubert JD, Leuenberger P (1997) Peptidases in human bronchoalveolar lining fluid, macrophages, and epithelial cells Dipeptidyl (amino)peptidase IV, aminopeptidase N, and dipeptidyl (carboxy)peptidase (angiotensin-converting enzyme). J Lab Clin Med 130(6) 603—614. 

MC 1 Family (including various carboxy-peptidases) Zn2+ Bound to His - Xaa- Xaa- (llu and another His a+(S sandwich... 

The resolution of a-methylvaline had not been reported at the time this work was done. Subsequently, Turk, et al. published the resolution of trifluoroacetyl-a-methylvaline by carboxy-peptidase A (O. Some comments on the absolute configuration of the amino acids will be made later. 

Elastase mainly cleaves on the C side of the aliphatic amino acids Gly, Ala, Val, and lie. Smaller peptides are attacked by carboxy-peptidases, which as exopeptidases cleave individual amino acids from the C-terminal end of the peptides (see p. 176). 

Carboxy Peptidase (MW = 34,300, 1 Zn) This enzyme in the pancreas of mammals catalyses the hydrolysis of the peptide bonded at the carboxyl end of a peptide chain. 

Ribonuclease Ti is fairly resistant to proteases. The threonine residue at the carboxyl terminal of the enzyme can be removed by carboxy-peptidase A without loss of activity (67). Leucine aminopeptidase does not release amino acids from the amino terminal (68). Ribonuclease Ti is not inactivated by trypsin or chymotrypsin in the presence of 0.2 M phosphate (69), which probably binds the enzyme and protects it from inactivation (67). Treatment of the enzyme with trypsin in the absence of phosphate inactivates it (67). Ribonuclease Tj is hydrolyzed by pepsin with progressive loss of activity (69). 

The substrate concentration dependence of the cobalt carboxy-peptidase B reactions has also been studied (96). With most of the investigated substrates, the higher activity of the cobalt enzyme as compared to the zinc enzyme is essentially expressed in larger values of Vmax, while Km-values are similar. 

Like many other useful discoveries, enzyme immobilization by cross-linking was actually an unintended by-product of another research project. In 1964, Florante Quiocho and Frederic Richards at Yale university cross-linked crystals of carboxy-peptidase-A with glutaraldehyde (pentane-1,5-dial), hoping to get stable crystals for X-ray diffraction studies. They noted that these cross-linked enzyme crystals (now... 

J. E. Hanson, A. P. Kaplan, and P. A. Bartlett. Phosphonate analogues of carboxy-peptidase A substrates ore potent transition-slate analogue inhibitors. Biochemistry 2 6294-6305 (1989). 

It is known that p-lactamase catalyzes the rapid hydrolysis of the p-lactam ring of penicillins and cepharosporines. The hydrolytic activity of these enzymes eliminates the bacteriocidal action of many p-lactam antibiotics and makes the organism resistant to these molecules. For this reason, the p-lactamase inhibitors have long been regarded as promising targets from a medicinal viewpoint. A comparison between the kinetic characteristics of p-lactamase and penicillin-sensitive enzymes (carboxy-peptidase and transpeptidase) is of interest in this respect. p-Lactamases very efficiently hydrolyze p-lactam in contrast to penicillin-sensitive enzymes [high /e4 in Eq. (9)]. 

Red Sepharose Procion Red NADP+-requiring enzymes Carboxy-peptidase G Pharmacia... 

ACE, Angiotensin Converting Enzyme is a peptidyl carboxy peptidase which forms the octapeptide angiotensin II from angiotensin I. Angiotensin II is a powerful pressor agent responsible for essential hypertension. Therefore, compounds that inhibit ACE are used in the treatment of hypertension. 

Metals are used not only as labels in histochemistry and immunochemistry, but also for studying protein structure and properties. Some metal ions can serve as valuable probes by replacing the original ions in different metaloenzymes or other metaloproteins. For instance, cobalt can replace zinc on the active side of carboxy-peptidase, aldolase, carbonic anhydrase, phosphatase or yeast alcohol dehydrogena. ... 

Figure 16. Hydrolysis rate of bovine ribonuclease relative to that of performic acid-oxidized ribonuclease as a function of temperature (155). The follotving enzymes were used O, aminopeptidase , carboxy-peptidase A A, trypsin and , chymotrypsin.

The specificities of the various digestive exo- and endopep-tidases suggest that they act synergistically to fulfill a major nutritional function. The concerted action of trypsin, chy-motrypsin, pepsin, and carboxypeptidases A and B facilitate and ensure formation of essential amino acids. The chemical characteristics and metalloenzyme nature of two bovine exopeptidases, lens aminopeptidase and pancreatic carboxy-peptidase A, indicate similarities in their mechanisms of action. However, the aminopeptidase exhibits an unusual type of metal ion activation not observed unth carboxy-peptidase. Chemical and physicochemical studies reveal that the latter enzyme has different structural conformations in its crystal and solution states. Moreover, various kinetic data indicate that its mode of action toward ester substrates differs from that toward peptide substrates. The active site metal atom of carboxypeptidase figures prominently in these differences. 

Studies in solution indicate that the conformations of tyrosine-248 in the dissolved and crystalline states may be quite different. This conclusion is based on the work of Johansen and Vallee. They have examined the absorption and circular dichroic spectral properties of a carboxy-peptidase A derivative in which tyrosyl-248 is selectively labeled with the conformational probe, diazotized arsanilic acid 62, 63),... 

The action of these two pancreatic exopeptidases on synthetic substrates, proteins, and peptides has been reviewed in detail by Neurath (1960). The specificity requirements which were deduced from studies with synthetic peptides have been confirmed by studies with polypeptides. The structural requirements of specific substrates for both types of carboxy-peptidase are analogous except for the nature of the amino acids which contain the free, ionized a-carboxyl group at the terminus of the substrate. Carboxypeptidase B hydrolyzes most rapidly those bonds formed by terminal lysyl and arginyl residues, whereas carboxypeptidase A hydrolyzes terminal bonds formed by a variety of aromatic, neutral, or acidic amino acids. Of the natural amino acids only carboxyl-terminal prolyl residues are resistant to the action of the enzyme. The rate of hydrolysis depends upon the nature of the side chains of the amino acids which form the susceptible bonds. Thus, differences in the rate of hydrolysis of different substrates may vary several thousandfold. The methods for application of these peptidases to hydrolysis of proteins have been discussed in detail by Canfield and Anfinsen (1963). 

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