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Angiotensin I-converting-enzyme-inhibitory and antibacterial peptides from Lactobacillus helveticus PR4 proteinase-hydrolyzed caseins of milk from six species

Minervini, F., Algaron, F., Rizzello, C.G., Fox, P.F., Monnet, V., Gobbetti, M.
Applied and environmental microbiology 2003 v.69 no.9 pp. 5297-5305
Lactobacillus helveticus, proteinases, enzymatic hydrolysis, enzyme activity, proteolysis, caseinates, milk, dairy animals, maternal milk, breast milk, casein hydrolysates, antimicrobial peptides, antibacterial properties, animal pathogenic bacteria, enzyme inhibitors, peptidases, bioactive properties, amino acid sequences
Sodium caseinates prepared from bovine, sheep, goat, pig, buffalo or human milk were hydrolyzed by a partially purified proteinase of Lactobacillus helveticus PR4. Peptides in each hydrolysate were fractionated by reversed-phase fast-protein liquid chromatography. The fractions which showed the highest angiotensin I-converting-enzyme (ACE)-inhibitory or antibacterial activity were sequenced by mass spectrum and Edman degradation analyses. Various ACE-inhibitory peptides were found in the hydrolysates: the bovine alphaS1-casein (alphaS1-CN) 24-47 fragment (f24-47), f169-193, and beta-CN f58-76; ovine alphaS1-CN f1-6 and alphaS2-CN f182-185 and f186-188; caprine beta-CN f58-65 and alphaS2-CN f182-187; buffalo beta-CN f58-66; and a mixture of three tripeptides originating from human beta-CN. A mixture of peptides with a C-terminal sequence, Pro-Gly-Pro, was found in the most active fraction of the pig sodium caseinate hydrolysate. The highest ACE-inhibitory activity of some peptides corresponded to the concentration of the ACE inhibitor (S)-N-(1-[ethoxycarbonyl]-3-phenylpropyl)-ala-pro maleate (enalapril) of 49.253 microgram/ml (100 micromol/liter). Several of the above sequences had features in common with other ACE-inhibitory peptides reported in the literature. The 50% inhibitory concentration (IC50) of some of the crude peptide fractions was very low (16 to 100 microgram/ml). Some identified peptides were chemically synthesized, and the ACE-inhibitory activity and IC50s were confirmed. An antibacterial peptide corresponding to beta-CN f184-210 was identified in human sodium caseinate hydrolysate. It showed a very large spectrum of inhibition against gram-positive and -negative bacteria, including species of potential clinical interest, such as Enterococcus faecium, Bacillus megaterium, Escherichia coli, Listeria innocua, Salmonella spp., Yersinia enterocolitica, and Staphylococcus aureus. The MIC for E. coli F19 was ca. 50 microgram/ml. Once generated, the bioactive peptides were resistant to further degradation by proteinase of L. helveticus PR4 or by trypsin and chymotrypsin.