Human angiotensinogen. Purification partial characterization, and a comparison with animal prohormones

The renin-angiotensin system appears to play a major role in the regulation of sodium excretion and fluid intake in a wide variety of animal species from mammals to teleosts. In mammals the system has evolved further importance in terms of blood pressure homeostasis. This hormonal system in all species appears to involve a serum protein prohormone, angiotensinogen, a proteolytic enzyme, renin, and angiotensin I, the decapeptide product of the reaction between renin and angiotensinogen. The importance of this system to the organism appears to correlate directly with the necessity to conserve sodium while an abnormality of this process may underlie the development of hypertension in man. As the starting point of the system, angiotensinogen assumes special importance as a possible index of evolutionary development. In addition, it has been known for many years that human (viz. primate) angiotensinogen differs from that found in other mammals in its inability to be a substrate for animal renins while animal angiotensinogens readily react with human renin. Thus, the enzymatic specificity appears to reside with the prohormone. The biochemical basis for this difference is unresolved due primarily to the lack of purified human angiotensinogen. In this paper we describe methods for the purification of human angiotensinogen which have direct applicability to animal angiotensinogens. Our approach utilizes ammonium sulfate precipitation, Sephadex G-150 chromatography, multiple isoelectric focusing, and concanavalin A-Sepharose affinity chromatography. With the availability of highly purified human angiotensinogen we compared the molecular weights, heterogeneity, isoelectric points, and thermal lability of hog, rabbit, and human angiotensinogen in order to define the biochemical basis of the species variation in renin reactivity...