Proline specificity

In addition to phosphotriesterase from P. diminuta (PTE) discussed above, two other types of enzymes were found to exhibit phosphotriesterase activity. Interestingly, both are peptidases - the enzymes which in nature hydrolyse a peptide bond. The first one - organophosphorus acid anhydrolase (OPAA) from Alteromonas sp. JD6.5 - is a proline dipeptidase its original activity is to cleave a dipepfide bond with a prolyl residue at the carboxy terminus. The second one - aminopeptidase P (AMPP) from Escherichia coli - is a proline-specific peptidase that catalyses hydrolysis of N-terminal peptide bonds containing a proline residue. ° ... 

Augustyns, K., der Veken, P.V., Senten, K. and Haemers, A. (2005) The therapeutic potential of inhibitors of dipeptidyl peptidase IV (DPP-IV) and related proline-specific dipeptidyl aminopeptidases. Current Medicinal Chemistry, 12, 971-998 (c) Augustyns, K., der Veken, P.V. and Haemers, A. 

Inhibitors of proline-specific dipeptidyl peptidases DPP-4 inhibitors as a novel approach for the treatment of type 2 diabetes. Expert Opinion on Therapeutic Patents, 15, 1387-1407 (d) von Geldern, T.W. and Trevillyan, J.M. 

Lopez, M. and Edens, L. (2005). Effective prevention of chill-haze in beer using an acid proline-specific endoprotease from Aspergillus niger.. Agric. Food Chem. 53, 7944 7949. McCarthy, S. L., Melm, G. D., and Pringle, A. T. (2005). Comparison of rapid physical stability tests. ]. Am. Soc. Brew. Chem. 63, 69-72. 

Since proline already contains a pyrrolidine ring it provides a potential source of nitrogen heterocyclics in the MaiUard reaction, and a number of proline-con-taining model systems have been examined. Tressl et al. [32] identified more than 120 proline-specific compounds in the reaction of proline or hydroxypro-line with various sugars. These include pyrrolines, pyrroles, pyridines, indolines, pyrrolizines and azepines, but relatively few of the compounds have been identified among food volatiles. 

The starter cells begin to die off at the end of curd manufacture (Figure 10.21) the dead cells may lyse and release their intracellular endopeptidases (Pep O, Pep F), aminopeptidases (including Pep N, Pep A, Pep C, Pep X), tripeptidases and dipeptidases (including proline-specific peptidases) which produce a range of free amino acids (Figure 10.22). About 150 peptides have... 

Many aminopeptidases are metalloenzymes.437 Most studied is the cytosolic leucine aminopeptidase which acts rapidly on N-terminal leucine and removes other amino acids more slowly. Each of the subunits of the hexameric enzyme contains two divalent metal ions, one of which must be Zn2+ or Co2+438/439 A methionine aminopeptidase from E. colt contains two Co2+ ions440/441 and a proline-specific aminopeptidase from the same bacterium two Mn2+.442 In all of these enzymes the metal ions are present as dimetal pairs similar to those observed in phosphatases and discussed in Section D,4 and to the Fe-Fe pairs of hemerythrin and other diiron proteins (Fig. 16-20). A hydroxide ion that bridges the metal ions may serve as the nucleophile in the aminopeptidases.438 A bound bicarbonate ion may assist.4383... 

J.-B. Charbonnier and A. M nez, Engineering cyclophilin into a proline -specific endopeptidase, Science 1998, 391, 301-304. 

Amino acid specific Maillard products were isolated from the extracts by preparative GC or HPLC and identified by MS-, IR-, 1 H- and c-NMR-spectroscopy. Proline derived components are important constituents in bread, malt and beer. More than 120 proline specific Maillard products were characterized. Cysteine and methionine derived components were predominant in roasted coffee and meat flavors. Thirty cysteine- and twenty methionine-specific Maillard products were identified for the first time. 

As demonstrated in previous publications, model reactions of L-proline and monosaccharides result in complex mixtures of proline specific compounds (J —4 ) During the Maillard reaction of L-proline and reducing sugars more than 120 proline specific compounds were identified by MS-, IR-, 1H- and 13c-NMR-spectroscopy (among them ... 

The products found in model experiments and in foodstuffs are not comparable. The concentrations of individual constituents vary considerably between both systems. Figure 4 summarizes proline specific components determined in wort and beer produced under different reaction conditions. Beer I represents a German pale beer, produced from pale malt by a conventional wort... 

Figure 4 Typical proline specific constituents in wort and beer depending on different boiling conditions...

Figure 10-2 Mode of Action of Proline-Specific Peptidases. Source Reprinted with permission from M.B. Habibi-Najafi and B.H. Lee, Bitterness in Cheese A Review, Crit. Rev. Food Sci. Nutr., Vol. 36, No. 5, p. 408. Copyright CRC Press, Boca Raton, Florida.

Currently isomer specificity is known as an important property in the action of proteases, protein phosphatases, and proline-specific protein kinases on their proteinaceous substrates in vitro and in vivo [174-176]. 

Protease, Proline-Specific Endopeptidase Origin Flavobacterium sp. Toyobo... 

Proline is the second most abundant amino acid (13-18%) contained in wheat gluten, and plays a very in rtant role in flavor formation during food processing. A great deal of work has been carried out by Tressl et aL (5) on the volatile conponents generated in proline-specific Maillard reactions. The most abundant proline-specific Maillard reaction products arc 2,3-dihydro-IH-pyrrolizines. 

Helak B., Spengler K., Tressl R. and Rewicki D. (1989a) Formation of 7//-cyclopenta[6]pyridin-7-ones as proline-specific Maillard products. J. Agric. Food Chem. 37, 400-4. 

Dihydro-IH-pyrrolizines are as proline specific Maillard products <85MI 801-01). 

The proline-specific aminopeptidase P(AMPP) specifically hydrolyzes the N-terminal amino acid from peptides in which the penultimate residue is a proline. It was earlier shown that AMPP from E. coli was activated by both Mn and Co +, and EPR and EXAFS spectra of the Mn +-reconstituted enzyme were consistent with the presence of a dinuclear center. Subse-... 

---