Phagocytosis and Pinocytosis in Acanthamoeba castellanii

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Abstract
Pseudomonas putida assimilates peptides and hydrolyses them with intracellular peptidases. Amino acid auxotrophs (his, trp, thr or met) grew on a variety of di-and tripeptides up to twice as slowly as with free amino acids. Pseudomonas putida has separate uptake systems for both dipeptides and oligopeptides (three or more residues). Although the dipeptide system transported a variety of structurally diverse dipeptides it did not transport peptides having either unprotonatable N-terminal amino groups, blocked C-terminal carboxyl groups, D-residues, three or more residues, N-methylated peptide bonds, or β-amino acids. Oligopeptide uptake lacked amino acid side-chain specificity, required a free N-terminal L-residue and had an upper size limit. Glycylglycyl-D, L-p-fluorophenylalanine inhibited growth of P. putida. Uptake of glycylglycyl[I-14C]alanine was rapid and inhibited by 2,4-dinitrophenol. Both dipeptide and oligopeptide uptake were constitutive. Dipeptides competed with oligopeptides for oligopeptide uptake, but oligopeptides did not compete in the dipeptide system. Final bacterial yields were 5 to 10 times greater when P. putida his was grown on histidyl di-or tripeptides rather than on free histidine because the histidyl residue was protected from catabolism by L-histidine ammonia-lyase.

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