A mixture of tetradecamer oligodeoxyribonucleotides complementary to the codons specifying the carboxylterminal sequence, Ile-His-Pro-Phe-His, of angiotensin was chemically synthesized as two pools and used for the isolation of a cDNA clone specific for angiotensinogen from a cDNA bank of rat liver mRNA sequences. The two pools (oligo 1 and oligo 2), each containing 24 oligodeoxyribonucleotides, were first used as primers to initiate reverse transcription of rat liver mRNA. One of the pools (oligo 1) was found to prime a specific 32P-labeled cDNA of approximately 160 nucleotides that contained the anticoding sequence corresponding exactly to the amino acid sequence of rat angiotensin. This cDNA, in turn, was used to rescreen cDNA clones that were isolated by initially selecting the rat liver cDNA bank by hybridization with the oligo 1 mixture. One clone thus obtained, designated pRagl6, was subjected to nucleotide sequence analysis and verified to contain a nearly full-length cDNA sequence coding for rat angiotensinogen precursor. The deduced amino acid sequence indicates that the precursor molecule consists of angiotensinogen of 453 amino acid residues and a putative signal peptide of 24 amino acid residues. The predicted molecular weight and amino acid composition of angiotensinogen agree well with those determined by using the purified protein. An angiotensin moiety is located at the amino-terminal part of angiotensinogen, preceded directly by the signal peptide and followed by a large carboxyl-terminal sequence that contains two internally homologous sequences and three potential glycosylation sites.Angiotensinogen (renin substrate), a glycoprotein mainly synthesized by the liver and secreted into the circulating blood, is cleaved by the enzyme renin (EC 3.4.99.19), thus releasing the decapeptide angiotensin I. The latter is then cleaved by angiotensin converting enzyme (dipeptidyl carboxypeptidase, peptidyldipeptide hydrolase, EC 3.4.15.1), forming the octapeptide angiotensin II. Angiotensin II is the principal biologically active peptide that causes arteriolar vasoconstriction and stimulates aldosterone secretion from adrenal cortex (reviewed in refs. 1 and 2). Angiotensin formation has also been shown to occur in the central nervous system, where angiotensin appears to be involved in causing thirst and in control of the secretion of vasopressin and corticotropin (ACTH) (3). Through these actions, the renin-angiotensin system plays an important role in the control of blood pressure and hydromineral balance. Evidence is accumulating that the level of angiotensinogen in the circulation is as important as that of renin in determining the rate of formation of angiotensin and therefore the activity of the renin-angiotensin system (1). Angiotensinogen production is regulated by several factors such as glucocorticoids, estrogens, and angiotensin II (1, 4). However, the mechanisms responsible for the regulation of angiotensinogen production have not been elucidated.Recently, angiotensinogen has been purif...

No abstract

No abstract

No abstract

No abstract