Tachyplesin I, a cationic heptadecapeptide amide containing two disulfide bonds isolated from hemocytes of Tuchypleus tridentutus, which binds to lipopolysaccharide, was synthesized by a solid-phase procedure. Reduction and oxidation of the deprotected peptide amide yielded an identical pcptide to native tachyplesin I in terms of chemical and biological properties. Tachyplesin I was found to bind to alkylphosphorylcholine accompanied by perturbation of its tyrosyl and tryptophyl residues but bound only weakly to N-acetyl-D-glucosamine tetramer.

Three peptides containing the putative Ca2+ binding loops, I, II and III, respectively, of a photoprotein, aequorin, from jellyfish Aequorea victoria were synthesized by a solid‐phase procedure. The peptides bound Ca2+ with dissociation constants or 10−3 to 10−4 M, providing evidence for the assumption that Ca2+ binding loops are actually responsible for the binding of Ca2+. When the highly conserved 6th glycine residue in the 12‐residue loops was replaced by arginine, no large effect was observed on Ca2+ binding. Exposure to a hydrophobic environment and the binding or Ca2+ brought about conformational changes to the peptides.

When Trimeresurus flavoviridis phospholipase A2 was reacted with methyl p-nitrobenzenesulfonate, its activity decreased following first-order kinetics. The pH dependence of the rate constants of inactivation showed that His-48 with an apparent pKa of 6.5 controls the reaction. In the pH region below 6.5, N1-methylhistidine was predominantly formed. On the other hand, N1,N3-dimethylhistidine was almost exclusively produced in the pH region above 6.5. No N3-methylhistidine was detected at any pH tested. Such observations suggested that the first methylation occurred at the N1-position of the imidazole ring followed by a second methylation at the N3-position, and that His-48 couples the carboxylate of Asp-99 at the N3-position of the imidazole ring, in accord with the interaction observed in the crystal structure of homologous Crotalus atrox phospholipase A2. As it has been reported that, in the reaction of chymotrypsin with methyl p-nitrobenzenesulfonate at pH 7.8, only monomethylation occurred at the N1-position of the His-57 imidazole group (Nakagawa, Y. & Bender, M.L. (1970) Biochemistry 9, 259-267), the nature of the active site histidine-aspartate couple of T. flavoviridis phospholipase A2 seems not to be identical with that of chymotrypsin.