Peptide and amino acid transport in Streptococcus bovis.

In amino acid transport studies with Streptococcus bovis using 14C-labelled amino acids, it has been shown that between 87% and 95% of cell-associated radioactivity was located in the cytosol. In similar studies with unlabelled peptides, most test peptide associated with S. bovis was truly intracellular. Using sodium dodecyl sulphate-polyacrylamide gel electrophoresis, the proteolytic activity in S. bovis was found to be largely cell-associated and of the serine-protease type, but stimulated by dithiothreitol. A wide range of extracellular peptide hydrolysing activities was demonstrated against the pentapeptide Leu-Trp-Met-Arg-Phe, which was completely hydrolysed to eight products after 10 min incubation. Some of this pentapeptide was transported intact, indicating the existence of mechanisms for the transport of peptides up to 751 Da. In studies with Arg-Phe-Ala, only Phe (F) and Ala (A), and to a much lesser extent Phe-Ala (FA) were transported after extracellular hydrolysis to FA, Arg (R), F and A. In this case, amino acid transport was much more predominant than peptide transport. The extent and nature of peptide transport was affected by the addition of protease inhibitors.