The amino acid sequence of hypertensin. II

Clinical connotations of the experimental hypertensions

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Renal pressor system in hypertension; evidence for circulating hypertensin in chronic renal hypertension; nature and activity of purified hypertensin

Hypertensin has been found in the circulating arterial blood in dogs with experimental renal hypertension and in human beings with essential hypertension. Two different chemical forms of the material have been obtained in purified form and their chemical constitution determined. The decapetide hypertensin I is the initial product of the action of renin on its substrate. This material is transformed to the vasoconstrictor octapeptide hypertensin II by a chloride activated enzyme of the plasma.

Synthesis and properties of angiotonin

Angiotonin has been shown to be formed by a converting enzyme in blood by the splitting off of the 2 amino acids histidine and leucine from the inactive decapeptide (asp-arg-val-tyr-ileu-his-prol-phe-his-leuc). The synthesis of the active octapeptide is described and its pharmacologic resemblance to the natural product is demonstrated.

Pressor polypeptides formed in vivo and in vitro as mediators of renal hypertension

During the purification of hypertensin formed in vitro, evidence of heterogeneity of the pressor activity was obtained by counter current distribution. Pepsitensin shows a similar heterogeneity. These facts lead to the hypothesis that other proteolytic enzymes may also be present in the tissues and may hydrolyze hypertensinogen with the formation of pressor polypeptides of the hypertensin or pepsitensin type. Thus, substances similar to hypertensin may be formed in the organism by the action of proteolytic enzymes other than renin and may, if produced locally, exert a vasoconstrictor action or, if they enter the circulation, cause an increase in blood pressure.

The preparation, purification, and amino acid sequence of a polypeptide renin substrate

A purified preparation of a polypeptide renin substrate prepared by tryptic degradation of the protein renin substrate has been analyzed by the fluorodinitrobenzene method and after degradation with renin, carboxypeptidase, and phenylisothiocyanate, has been found to possess the amino acid sequence; asp-arg-val-tyr-ileu-his-pro-phe-his-leu-leu-val-tyr-ser. The first 10 of these amino acids constitutes hypertensin I which is released by cleavage of the leucyl-leucine bond by renin. The remaining 4 amino acids, leu, val, tyr, ser, apparently link hypertensin I to the protein renin substrate.