Abstract
Inhibitory effects of various amino acid esters on the phagocytic activity of guinea pig peritoneal macrophages were studied with sensitized 51Cr-sheep erythrocytes (51Cr-EAb) as well as 125I-α-amylase complexed with homologous IgG2 antibody (Ag-Ab complex). The intracellular uptake of 51Cr-EAb was markedly inhibited by N-acetyl-L-phenylalanine ethyl ester (Ac-Phe-OEt), N-acetyl-L-tryptophan ethyl ester (Ac-Trp-OEt) and N-benzoyl-L-tyrosine ethyl ester (Bz-Tyr-OEt), but not by N-acetyl-L-tyrosine ethyl ester (Ac-Tyr-OEt), N-α-acetyl-L-arginine methyl ester (Ac-Arg-OMe), N-α-benzoyl-L-arginine ethyl ester (Bz-Arg-OEt) or N-α-acetyl-L-lysine methyl ester (Ac-Lys-OMe).
When phagocytosis of the Ag-Ab complex was assayed by measuring the amount of digested products released from macrophage cells, Ac-Tyr-OEt also inhibited it as markedly as Ac-Phe-OEt, Ac-Trp-OEt, and Bz-Tyr-OEt did, whereas Bz-Arg-OEt again did not show any effect. The results of analysis of the intracellular fate of the Ag-Ab complex taken up by macrophages through the use of analytical density gradient fractionation of the homogenized cells suggest that AcPhe-OEt inhibits the ingestive process since the distribution of Ag-Ab complex showed a single peak, closely accompanying the plasma membrane. Ac-Tyr-OEt, on the other hand, caused a marked accumulation of Ag-Ab complex in the lysosome fraction, reflecting the inhibition of intralysosomal digestion of the complex.
These results may classify the chymotrypsin substrates tested, into three groups: 1) Ac-Phe-OEt and Ac-Trp-OEt inhibiting the ingestive process in phagocytosis, probably more strongly than the digestive process; 2) Bz-Tyr-OEt inhibiting both the ingestive and digestive processes; and 3) Ac-Tyr-OEt inhibiting the digestive process alone. In addition, this classification of the chymotrypsin substrates may support the hypothesis that a certain chymotrypsin-like serine protease with a high substrate-specificity is involved in the ingestive process of immune complexes in macrophages.
