The dipole interaction model, treated by the partially dispersive normal mode method, is used to calculate circular dichroic spectra of cyclo(Gly-Gly), cyclo (Ala-Gly), cyclo(Ala-Ala), cyclo(Pro-Gly), cyclo(Pro-Ala), cyclo(Pro-Val), cyclo (Pro-D-Val), and cyclo(Pro-Pro) in the amide π-π* absorption band near 190 nm. Assuming a standard backbone geometry, spectra which are in fair to good agreement wth experiment are obtained for these molecules. The spectra are predicted to be sensitive to conformations of Pro and Val side chains. The effects of dipeptide ring folding on calculated CD spectra are mostly consistent with those found by other workers, except that it is found that a planar ring conformation of cyclo (Ala-Ala) and cyclo (Ala-Gly) gives predicted spectra comparable to experiment. The same model gives theoretical absorption spectra consistent with available experimental data. 相似文献
Purpose. Nitric oxide synthase (NOS) inhibitors such as Nitro-L-arginine (L-NA) are being considered for the management of hypotension observed in septic shock. However, little information is available regarding the pharmacokinetic and pharmacodynamic properties of these agents. Our objective was to examine the relationships between L-NA plasma concentration and various hemodynamic effects such as cardiac index (CI), mean arterial pressure (MAP), and heart rate (HR) elicited by L-NA administration in rats.
Methods. L-NA was infused at doses between 2.5 – 20 mg/kg/hr in anesthetized rats over one hour. Hemodynamic effects and plasma L-NA levels were determined.
Results. Infusion of L-NA resulted in dose-dependent increases in MAP and systemic vascular resistance (SVR), decreases in CI, and minimal change in HR. The relationships between the hemodynamic effects and plasma L-NA levels were not monotonic, and hysteresis was observed. Using nonparametric analysis, the equilibration half-time (t1/2,keo) between plasma L-NA and the hypothetical effect site was determined to be 51.5 ± 6.6 min, 42.4 ± 10.1 min, 43.4 ± 9.0 min for MAP, CI, and SVR, respectively (n = 14). The Emax and EC50 values obtained were + 32.5 ± 8.4 and 2.6 ± 1.3 g/ml for MAP and –52.9 ± 15.6 and 3.7 ± 1.8 g/ml for CI, respectively.
Conclusions. Although L-NA can bring about beneficial elevation of MAP, such effect is always accompanied by a stronger effect on CI depression. Dose escalation of L-NA may bring about detrimental negative inotropic effect and loss of therapeutic efficacy. 相似文献
Parthenolide (PTL) and micheliolide (MCL) are sesquiterpene lactones with similar structures, and both of them have been reported to exhibit multiple biochemical and pharmacological activities. This study aims to investigate the inhibition of these two compounds on the activity of UDP-glucuronosyltransferases (UGTs).
In vitro incubation mixture for recombinant UGTs-catalyzed glucuronidation metabolism of 4-methylumbelliferone (4-MU) was utilized to investigate the inhibition potential. Inhibition kinetics (including inhibition type and parameters) were determined, and in silico docking was employed to elucidate the inhibition difference between PTL and MCL on UGT1A1.
MCL showed no inhibition toward all the UGT isoforms, and PTL showed strong inhibition toward UGT1A1. The half-maximal inhibitory concentration (IC50) of PTL on the activity of UGT1A1 was determined to be 64.4?μM. Inhibition kinetics determination showed that PTL exerted noncompetitive inhibition toward UGT1A1, and the inhibition kinetic constant (Ki) was determined to be 12.1?μM. In silico docking method has been employed to show that hydrogen bonds between PTL and the activity cavity of UGT1A1 contributed to the stronger inhibition of PTL on the activity of UGT1A1 than MCL. In conclusion, PTL can more easily induce drug–drug interaction (DDI) with clinical drugs mainly undergoing UGT1A1-catalyzed glucuronidation.