No abstract

The substrate specificity of the catalytic subunit of rabbit skeletal muscle 3':5'-cyclic AMP-dependent protein kinase (EC 2.7.1.37; ATP:protein phosphotransferase) has been studied using the synthetic peptide Arg-Gly-Tyr-SerLeu-Gly corresponding to the sequence around serine 24, a phosphorylation site in reduced, carboxymethylated, maleylated (RCMM) chicken egg white lysozyme. This peptide served as a substrate for the enzyme and exhibited a 6-fold higher Vmax and a 100-fold higher Km than RCMM-lysozyme.Replacement of the arginine with glycine, histidine, or lysine resulted in a dramatic reduction in the Vm.x. These results support the concept that arginine is an important residue in determining the substrate specificity of the protein kinase, predominantly influencing the Vmax of the phosphorylation reaction. Two synthetic peptides in which serine was replaced by an alanine acted as competitive inhibitors of phosphorylation of the synthetic peptide substrate and RCMMlysozyme.Recent studies in this (1, 2) and other (3,4) refs. 1 and 2). The proximity of basic residues to the phosphorylation site has been noted by other authors (2,(4)(5)(6)(7)(8).In order to investigate further the role of arginine in protein kinase specificity a study of the phosphorylation of a variety of synthetic peptides was made. In this communication we report the effect of substituting other amino-acid residues for arginine in the hexapeptide, Arg-Gly-Tyr-Ser-LeuGly, corresponding to the amino acid sequence around serine 24 in chicken lysozyme. It is also reported that synthetic peptide analogs in which the serine has been replaced by an alanine act as competitive inhibitors of both peptide and protein phosphorylation. MATERIALS AND METHODSCyclic AMP-Dependent Protein Kinase. Homogeneous catalytic subunit of rabbit skeletal muscle cyclic AMP-dependent protein kinase (Peak I) was prepared by the method of Beavo et al. (9). The catalytic subunit will be referred to simply as protein kinase.Solid Phase Synthesis of Peptides. The hexapeptide substrates were custom synthesized by Peninsula Laboratories and supplied in crude form following HF cleavage from the resin. The hexapeptide Arg-Gly-Ile-Ala-Leu-Gly was synthesized in this laboratory by the solid phase techniques as described by Gutte and Merrifield (10). The completed peptide was cleaved (HBr) from the resin and deprotected (catalytic hydrogenation) according to the procedures described by Stewart and Young (11). The following amino-acid derivatives [protected on the a-amino position with the t-butoxycarbonyl (Boc) group] were purchased from Peninsula Laboratories: Boc-Ala, Boc-Arg(NO2),. Boc-Gly, Boc-Leu, Boc-Ile, Boc-Ser(Bzl).Purification of Synthetic Peptides. The deprotected synthetic hexapeptides were purified by ion exchange chromatography on a SP-Sephadex (1.5 X 100 cm) column eluted with a concave gradient (0.2-2.0 M) of pyridine-acetate buffer, (pH 3.1-3.65) at 500. The peptide material present in the column effluent was detected with fluorescamine (Fluram, Roche Dia...

No abstract

Previously, it was shown that arthroconidia of Coccidioides immitis appear to inhibit phagosome-lysosome fusion and survive within normal mouse peritoneal macrophages. However, when these macrophages are exposed to antigen-stimulated T lymphocytes from immune mice, activation occurs, leading to enhanced phagosome-lysosome fusion and killing of C. immitis. Results indicate that the activation of macrophages can be effected after incubation with soluble lymphocyte product(s) (lymphokines). The activation of macrophages results if the macrophages are exposed to the lymphokine before, but not after, infection. The results indicate that the lymphocyte population responsible for the elaboration of the lymphokine is phenotypically Lytl 2-and that activation of macrophages by the lymphokine can occur across H-2 histocompatibility barriers.

No abstract