Binding of Cu+ and Cu2+ with peptides: Peptides = oxytocin, Arg8 -vasopressin, bradykinin, angiotensin-I, substance-P, somatostatin, and neurotensin.

The intrinsic binding ability of 7 natural peptides (oxytocin, arg8 -vasopressin, bradykinin, angiotensin-I, substance-P, somatostatin, and neurotensin) with copper in 2 different oxidation states (CuI/II ) derived from different Cu+/2+ precursor sources have been investigated for their charge-dependent binding characteristics. The peptide-CuI/II complexes, [M – (n-1)H + nCuI ] and [M – (2n-1)H + nCuII ], are prepared/generated by the reaction of peptides with CuI solution/Cu-target and CuSO4 solution and are analyzed by using matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. The MALDI mass spectra of both [M – (n-1)H + nCuI ] and [M – (2n-1)H + nCuII ] complexes show no mass shift due to the loss of ─H atoms in the main chain ─NH of these peptides by Cu+ and Cu2+ deprotonation.
The measured m/z value indicates the reduction of CuI/II oxidation state into Cu0 during MALDI processes. The number and relative abundance of Cu+ bound to the peptides are greater compared with the Cu2+ bound peptides. Oxytocin, arg8 -vasopressin, bradykinin, substance-P, and somatostatin show the binding of 5Cu+ , and angiotensin-I and neurotensin show the binding of 7Cu+ from both CuI and Cu targets, while bradykinin shows the binding of 2Cu2+ , oxytocin, arg8 -vasopressin, angiotensin-I, and substance-P; somatostatin shows the binding of 3Cu2+ ; and neurotensin shows 4Cu2+ binding. The binding of more Cu+ with these small peptides signifies that the bonding characteristics of both Cu+ and Cu2+ are different. The amino acid residues responsible for the binding of both Cu+ and Cu2+ in these peptides have been identified based on the density functional theory computed binding energy values of Cu+ and the fragment transformation method predicted binding preference of Cu2+ for individual amino acids.

Induction of uPA release in human peripheral blood lymphocytes by [deamino-Cysl,D-Arg8]-vasopressin (dDAVP).

[deamino-Cys(l),d-Arg(8)]-vasopressin (dDAVP), known to be an arginine vasopressin (AVP) V(2) receptor agonist, is an agent that increases fibrinolytic activity levels in plasma after its infusion into the human body. However, mechanisms underlying an increase and exact localization of the extrarenal dDAVP-responsive V(2) receptor remain unclarified. Two AVP receptors, V(1a) and V(2), and a related oxytocin (OT) receptor were found to be expressed in human lymphocytes. Furthermore, we found an increase of fibrinolytic activity in the medium of peripheral lymphocytes obtained from human volunteers less than 20 min after dDAVP infusion. The increased activity was also detected in the medium after incubating the lymphocytes in the presence of dDAVP in vitro, being highest at 20 min after the incubation. In accord with the increased fibrinolytic activity, the levels of urokinase-type plasminogen activator (uPA) in the medium were also increased.
However, there was no significant difference of plasminogen activator inhibitor-1 (PAI-1), pro-uPA, and tissue-type plasminogen activator (tPA) concentrations in the medium between dDAVP treatment and control. When lymphocytes were preincubated with a V(2) receptor antagonist [Adamantaneacetyl(1),O-Et-d-Tyr(2),Val(4),Aminobutyryl(6),Arg(8,9)]-vasopressin, the dDAVP-induced uPA increase was diminished. In contrast, preincubation with a V(1) receptor antagonist, [beta-Mercapto-beta,beta-cyclopentamethylenepropionyl(1),O-Me-Tyr(2),Arg(8)]-vasopressin, prior to dDAVP treatment resulted in a greater increase of the uPA concentration in the medium than with the dDAVP treatment alone. Thus it was suggested that dDAVP may induce uPA release from human lymphocytes via V(2) receptor-mediated reaction, and also via cross-talk between V(1) and V(2) receptors.

Effects of [Arg8]-vasopressin on regional cerebral blood flow in spontaneously hypertensive rats.

The effects of [Arg(8)]-vasopressin (AVP) and related compounds on regional cerebral blood flow (rCBF) in the hippocampus were studied using conscious spontaneously hypertensive rats (SHR). rCBF in the hippocampus decreased gradually with age in proportion to an increase in mean blood pressure. Subcutaneous injection of AVP caused a dose-dependent increase in rCBF in the hippocampus. The effects of the metabolic fragments AVP4-9 and AVP4-8 on rCBF were relatively weak. OPC-31260, a vasopressin V(2) antagonist, antagonized the AVP-induced increase in rCBF in the hippocampus.
Furthermore, subcutaneous injection of DDAVP, a V(2) agonist, increased rCBF in the hippocampus. On the other hand, the AVP-induced increase in rCBF in the hippocampus was not antagonized by OPC-21268, a vasopressin V(1) antagonist. Intracerebroventricular injection of AVP caused no significant changes in rCBF in the hippocampus, even at a dose of 10 ng/site.

[Arg8]-vasopressin-induced responses on coronary and mesenteric arteries of rats with myocardial infarction: the effects of V1a- and V2-receptor antagonists.

After myocardial infarction, plasma levels of [Arg8]-vasopressin rise to recover hemodynamics. The vascular responses to [Arg8]-vasopressin were studied in vitro in isolated hearts and mesenteric artery segments of rats with 1-day and 3-week-old infarcts, in absence and presence of the V1a-receptor antagonist SR-49059 and the V2-receptor antagonist OPC-31260. Vascular responses of coronary arteries were similar in sham and infarcted hearts. On average, coronary flow was maximally decreased by 70 +/- 3% from baseline values of 11.1 +/- 0.3 ml/min, with pD2 values of 10.52 +/- 0.05.
In mesenteric artery segments of sham and infarcted rats, maximal contractile forces, expressed as percentage of contraction to 125 mM KCl, were similar (232 +/- 23% and 239 +/- 8%, respectively). However, pD2 values from infarcted rats (9.22 +/- 0.07) were significantly lower compared with sham (9.55 +/- 0.07) rats. In coronary as well as mesenteric vessels, the vasoconstrictor responses, being more susceptible to SR-49059 (apparent pA2, between 9.12 and 9.82) than to OPC-31260 (apparent pA2, between 6.21 and 6.92), seemed mediated by the V1a receptor. These data indicate that in mesenteric but not in coronary vessels, an altered responsiveness to vasopressin could be observed. Responses are mediated mainly by the V1a receptor.

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Structure determination of [Arg8]vasopressin methylenedithioether in dimethylsulfoxide using NMR.

The structure of [Arg8]vasopressin methylenedithioether ([AVP]CH2) has been determined in dimethylsulfoxide-d6. Two-dimensional DQF-COSY and NOESY spectra were measured and used to derive angle and distance constraints for restrained molecular dynamics (MD) calculations. In the MD trajectory, two types of beta-turn structure were found in the region from Tyr2 to Asn5, suggesting an equilibrium between type-I and type-II’ beta-turn structures. When Halpha chemical shifts were used as an additional constraint, the type-I turn was favoured.
To validate this result, an independent energy minimization procedure was used, using differences between calculated and observed chemical shifts. The two approaches gave essentially identical results. It is therefore concluded that the type-I turn predominates in solution. Analysis of calculated chemical shift contributions suggests that the beta-turn structure found in AVP is well preserved in [AVP]CH2, although the pressin ring size is expanded.

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