SUMMARY: possesses permeases that specifically transport exogenous peptides with a free or α-N-methylated terminal amino group, but not with a terminal acyl group. To determine whether steric hindrance or loss of positive charge might be responsible for inactivity of acyl peptides we prepared and tested a series of α-N-alkyl peptides, several with alkyl substituents larger than the inactivating acyl groups. α-N-dimethyl, -ethyl, -propyl, -butyl, -isopropyl and -isobutyl peptides were prepared by NaBH treatment of aldehyde or ketone-peptide complexes. The positively charged monoalkyl derivatives of triglycine were all nutritionally active, all competed with unsubstituted peptides, and all failed to be absorbed by a mutant that lacked the oligopeptide permease. Dimethyltriglycine was nutritionally and competitively inactive. The results negate the explanation of steric hind-rance and suggest a requirement for an N-terminal α-amino hydrogen for peptide transport.


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