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Metabolism of small peptides in rumen fluid. Accumulation of intermediates during hydrolysis of alanine oligomers, and comparison of peptidolytic activities of bacteria and protozoa
Author(s) -
Wallace R John,
McKain Nest,
Newbold C James
Publication year - 1990
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.2740500207
Subject(s) - rumen , bacteria , hydrolysis , biochemistry , protozoa , chemistry , metabolism , alanine , peptide , oligopeptide , biology , amino acid , microbiology and biotechnology , fermentation , genetics
Oligopeptides of L ‐alanine up to ala 5 , were incubated in vitro in either strained rumen fluid or suspensions of mixed rumen bacteria. The disappearance of substrates and formation of products were measured for 40 min, by which time ala 3 , ala 4 and ala 5 were almost totally hydrolysed. Ala 2 was more slowly hydrolysed, and accumulated in incubations with the other peptides. The pattern of formation of ala 2 but not ala 3 from ala 4 , and ala 3 and ala 2 but not ala 4 from ala 5 , suggested that the peptides were being hydrolysed by a dipeptidyl peptidase mechanism. Three different sheep receiving different diets gave similar results. Neither substrates nor products appeared to be accumulated intracellularly, except for ala 2 , and then only if protozoa were present. Protozoa were more active than bacteria in ala 2 hydrolysis, whereas bacteria had greater activities with higher homologues. Similar preferences were observed with glycine peptides, although unlike alanine peptides gly 3 and gly 5 were more slowly degraded than the dimer. These experiments suggest that protozoa are of importance in the accumulation and hydrolysis of dipeptides, whereas bacteria are responsible for the breakdown of larger molecules by a dipeptidyl peptidase mechanism that does not appear to involve accumulation within the cell.