[Contractile activities of synthetic bradykinin fragments on guinea pig ileum]

Biochemical problems of regulation by oligopeptides

Some problems are considered which arise in biochemical studies on structure and function of natural oligopeptides consisting of 2-50 amino acid residues. The problems under consideration include the generation of oligopeptides from precursors, chemical structure, the role of functionally important radicals and spatial configuration, and structure-function relationships. Different types of regulation are shown mainly for oligopeptides involved in muscle contraction.

Comparative studies on the properties of a kininase in rat brain using bio- and fluorometric assay systems

The properties of rat brain kininase that degrade bradykinin (BK) at the Phe5-Ser6 peptide bond were compared using two different assay systems. After an enzymatic reaction, the residual BK was bioassayed using a guinea pig ileum. BK and its degraded products were also determined fluorometrically by the combined procedures of microdansylation and thin-layer chromatography. The optimal pH of the kininase was within the neutral range in both assay systems. In the bioassay system, EDTA activated the kininase without dependency on its concentrations, while sulfhydryl (SH) reagents tended to inhibit the activity at a high concentration. However, in the fluorometric assay system, EDTA did not show any effect, while SH reagents activated the kininase. Furthermore, SQ14225 did not inhibit the kininase even at a high concentration. The effect could not be determined by bioassay because the compound increased the potential for a contractile response of the ileum induced by BK. These findings suggest that the results obtained using a bioassay should be compared with those from a chemical assay for the exact elucidation of the nature of some kininases.

Cyclic analogue of bradykinin possessing selective and prolonged biological activity

Cyclo-[(N epsilon 1-Lys1, Gly6)-bradykinin] and its deprotected non-cyclic precursor, PheGlyProPheArg LysProProGly, were synthesized using the conventional methods of peptide chemistry. Similar to bradykinin, the cyclopeptide elicits a depressor reaction in rats, as revealed by the experiments in vivo. Its duration of action, however, is greater by several orders of magnitude. At the same time, it appears to exhibit no myotropic activity when applied in vitro to extravasal smooth muscle preparations (uterus and ileum of the rat). The non-cyclic precursor lacks the depressor activity, but produces a slight myotropic effect (alpha = 0.6 +/- 0.09; pD2 = 5.9 +/- 0.17).