Synthetic Tetradecapeptide Research Articles

Facilitation of adrenergic transmission by locally generated angiotensin II in rat mesenteric arteries.

When studied on isolated rat mesenteric arteries perfused with Tyrode's solution, angiotensin I and angiotensin II (1 ng/ml), a synthetic tetradecapeptide renin substrate, and a purified hog renin substance (50-100 ng/ml) potentiated vasoconstrictor responses to sympathetic nerve stimulation and to injected norepinephrine without altering basal pressure. These agents produced a greater augmentation of the vasoconstrictor responses to nerve stimulation than to injected norepinephrine. The potentiation of vasoconstrictor responses to sympathetic nerve stimulation and injected norepinephrine which was elicited by renin substrate and angiotensin I was abolished by an inhibitor of angiotensin I-converting enzyme, SQ 20,881, and by an angiotensin II receptor antagonist, [Sar1-Ile8]angiotensin II. In contrast, the potentiating effect of angiotensin II was blocked only by the latter compound. We conclude that utilization of renin substrate within the vascular wall by renin or renin-like enzymes results in the formation of angiotensin I, which is converted to angiotensin II. Angiotensin in turn potentiates the vasoconstrictor responses to adrenergic stimuli presumably by augmenting release of the adrenergic transmitter and inhibiting its neuronal reuptake as well as by increasing vascular reactivity to norepinephrine.

Angiotensin I [Phe 8-His 9] hydrolase - studies with renin substrates

Angiotensin I [Phe 8-His 9] hydrolase produced a pressor substance (probably angiotensin II) from synthetic tetradecapeptide renin substrate but not from human renin substrate. The activity of angiotensin I [Phe 8-His 9] hydrolase was effectively inhibited by cupric ion. Tetradecapeptide renin substrate was also shown to competitively inhibit angiotensin I hydrolysis by angiotensin I [Phe 8-His 9] hydrolase.

Angiotensin-forming enzyme in human brain

The subcellular and regional distribution of angiotensin-forming enzyme was examined in human brain. A relatively purified form of this enzyme was obtained by discontinuous sucrose density gradient subfractionation of the crude mitochondrial fraction. Of the six brain regions examined, the cerebellar cortex crude mitochondrial fraction had the highest angiotensin-forming enzyme content. Kinetic characteristics, with respect to hog plasma renin and synthetic tetradecapeptide substrates and optimum pH range (4·5–5·5), were similar for both the particulate and soluble forms of the enzyme. Both forms also had a lower affinity for human plasma renin substrate. Different substrate kinetics and optimum pH range were obtained for the brain angiotensin-forming enzyme and kidney renin. Because of its potential clinical implication, a brain renin-angiotensin-aldosterone system, which is independent of kidney and adrenals, merits further study.

Action of angiotensins and synthetic renin substrate on isolated rat colon.

AIKEN and Vane have reported1 the independent actions of angiotensin I (AI) and angiotensin II (AII) on various isolated smooth muscle preparations, including rat colon. Tney showed that the apparent contractile action of AI on these preparations depended primarily on its in situ conversion to All by “converting enzyme” and that when the activity of the enzyme was inhibited by a pentapeptide extracted from Bothrops jararaca venom, the residual contractile action, probably due to unchanged AI, was very small. I have investigated the action of synthetic tetradecapeptide renin substrates (TPRS) on rat colon, in the light of the known actions of AI and All.

Conformational transition of the synthetic 2–15 N-terminal fragment of hen egg-white lysozyme

It has been proposed [ 1 ] that the folding of a protein molecule begins at the amino end even before the synthesis is complete. Such a sequential mechanism presumes that the protei’n conformation is primarily due to interactions between amino acid residues close in the sequence and implies that parts of the polypeptide chain, particularly those near the terminal amino end, may fold into stable conformations that can still be recognized in the complete molecule and act as ‘internal templates’ around which the rest of the chain is folded. The results obtained by studying the conformational properties of the N-terminal eicosapeptide (S-peptide) [2, 31 of bovine pancreatic ribonuclease and of several S-peptide synthetic analogs [4] in aqueous solution and in the presence of helicogenic solvent, do not agree with the hypothetical sequential mechanism mentioned above. The hen egg-white lysozyme was shown by X-ray analysis [5] to contain three runs of helix (residues 515,24-34 and 88-96) for which the axial translation per residue and the number of residues per turn fall close to the a-helix values. The aim of the present paper is to report some preliminary conformational studies on the synthetic tetradecapeptide corresponding to the 2-l 5 N-terminal fragment of hen egg-white lysozyme. The peptide conformation has been investigated by circular dichroism in aqueous solution and in the presence of trifluoroethanol which is known to cause a transition from the random to the helical form in polypeptide systems.

The effect on drinking of peptide precursors and of shorter chain peptide fragments of angiotensin II injected into the rat's diencephalon.

1. Recently it has been shown that injection of angiotensin II into the anterior diencephalon causes the rat to drink water. In the present experiments the dipsogenic action of a number of other substances including substances related to angiotensin was tested.2. Injection of 0.001 Goldblatt u. renin into the angiotensin-sensitive region causes the water-replete rat to drink. Drinking is slower in onset and continues for longer than after injection of angiotensin II.3. Synthetic tetradecapeptide renin substrate and angiotensin I were as effective as angiotensin II at causing water-replete rats to drink.4. beta-aspartic acid(1)-valine(5)-angiotensin II was also fully effective; but the D-arginine substituted octapeptide was much less effective.5. The (2-8) heptapeptide retained about 50% of the dipsogenic activity of the octapeptide, whereas the absence of phenylalanine at the other end of the peptide chain in the (1-7) heptapeptide results in an inactive compound.6. The (3-8) hexapeptide and the (4-8) pentapeptide, both of which have phenylalanine at the end of the chain, and the (1-4) and (5-8) tetrapeptide fragments of angiotensin II showed only a slight action on intake of water.7. Kallikrein, bradykinin, adenosine-3'5-cyclic phosphate, vasopressin and oxytocin caused no drinking when injected into the angiotensin-sensitive region.8. It is concluded that the requirements for the dipsogenic activity of angiotensin are the same as those for its other biological actions with the qualification that the precursor peptides are also active, presumably because they give rise to angiotensin II locally.

Pseudorenin. A new angiotensin-forming enzyme.

A new enzyme, pseudorenin, has been discovered which resembles renin in its ability to form angiotensin I from the synthetic tetradecapeptide renin substrate and from purified hog renin substrate A. Its maximal activity occurs at a much lower pH value than does that of renin. The two enzymes may be easily separated by DEAE-cellulose chromatography. Unlike renin, pseudorenin does not attack substrate A in the presence of serum, nor does it produce angiotensin I from renin substrate as it exists in serum. In contrast to renin, which occurs primarily in the kidney, pseudorenin has been found in every one of the 13 different tissues which have been tested, and also in the plasma. The natural substrate for the new enzyme as well as its physiological function are not known.