Herman R. Wyssbrod

Reference lineshape adjusted difference NMR spectroscopy. II. experimental verification

Abstract The accuracy and reliability of difference NMR spectroscopy can be substantially improved by a simple correction based on changes in the lineshape of an internal reference line. This reference lineshape adjusted (RLSA) method is experimentally demonstrated to behave according to theoretical predictions under variations in drift of the main magnetic field, in rf power, in homogeneity of the main field, in spinning side bands, in detector phase, and in sweep rate. The RLSA method is experimentally demonstrated to automatically compensate for changes in all these instrumental parameters provided H, is sufficiently small that saturation is avoided. In addition, the internal reference must be constant in composition, concentration, and resonance position, and must be totally resolved from the rest of the spectrum. Under these conditions, the RLSA method is shown to give difference spectra that are visibly superior to simple difference spectra.

Confirmation of the solution structure of tyrocidine a using perturbation of proton relaxation rates by nitroxide spin labels

The spin–lattice relaxation rate enhancements of the protons of tyrocidine A upon addition of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) were analysed in solution and were shown to be consistent with the peptide conformation. The effects on tyrocidine A proton spin–lattice relaxation rates for three TEMPO derivatives in two different solvents have also been studied in order to obtain information about the influence of TEMPO substituents on nitroxide-biomolecule interactions. The neutral free radical TEMPO exhibits less specificity in its interaction with tyrocidine A than its derivatives and, hence, it is the most suitable probe for generally investigating conformational moieties of biomolecules in solution. By corollary, charged nitroxides should be probes of the microenvironment surrounding the specific site of interaction.

Molecular orbital studies of dimethyl diselenide

Results from theoretical studies of dimethyl diselenide (H3C–Se–Se–CH3) by semiempirical and ab initio molecular orbital (MO) methods are reported. The CNDO/2 method was employed for the semiempirical studies, and the restricted Hartree–Fock (RHF) method, in which an augmented STO‐3G basis set was used, for the ab initio studies. Total energy E was calculated as a function of a chosen internal coordinate (bond length, bond angle or torsion angle) by the CNDO/2 method while all other internal coordinates were held at fixed values. In addition, a geometric optimization in which selected internal coordinates were permitted to vary simultaneously was performed. The heights of the cis and trans torsional (rotational) barriers were calculated by the CNDO/2 method and found to be greatly exaggerated. More realistic values were calculated by the RHF method, in which an augmented STO‐3G basis set was used. The heights calculated by both MO methods were compared to the corresponding ones calculated by similar metho...

The assignment of the resonances of the backbone amide protons of arginine vasopressin and gramicidin S in D2O by decoupling during exchange

The resonances of six of the seven backbone amide protons of [8-arginine]vasopressin (AVP) and of all four nonequivalent backbone amide protons of gramicidin S (GS) in D2O were assigned by decoupling of the amide protons from their respective vicinal Cα protons while exchange of the amide protons for deuterons was occurring. The simple pulsed Fourier transform method involving only a (π/2-FID) sequence of pulses was used. This method of assigning resonances of exchangeable protons is termed on-the-fly decoupling. Values for the chemical shifts of the amide protons (δNH) and for the coupling constants between vicinal amide and Cα protons of AVP in D2O are shown to be quite similar to the corresponding ones previously published for [8-lysine]vasopressin in H2O at a slightly different acidity and temperature [J. D. Glickson, D. W. Urry, and R. Walter, Proc. Nat. Acad. Sci. USA 69, 2566 (1972)]. Values for the δNHS of GS in D2O are shown to be quite similar to the corresponding ones previously published for this peptide in CH3OH at the same temperature [D. W. Urry, in “The Enzymes of Biological Membranes” (A. Martonosi, Ed.), Vol. 1, pp. 31–69, Plenum, New York, 1976]. It is concluded that on-the-fly decoupling can be used to assign resonances of exchangeable protons in compounds dissolved at millimolar concentrations in solvents with exchangeable deuterons and that the spectral simplification that results when signals from rapidly exchanging protons are not observed may be advantageous.

STUDIES ON THE SOLUTION CONFORMATIONS OF NEUROHYPOPHYSEAL HORMONES: COMPARATIVE STUDIES OF [8-D-ARGININE]VASOPRESSIN AND [8-L-ARGININE]VASOPRESSIN IN D2O BY 1 H NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

[8-D-Arginine]vasopressin (DAVP), an active synthetic analog of the naturally occurring neurohypophyseal hormone [8-L-arginine]vasopressin (AVP), was studied in D 2 O at pD 3.3 and 23°C by 1 H nuclear magnetic resonance (NMR) spectroscopy, and chemical shifts (δs) and some of the coupling constants for the nonlabile protons (the protons that do not readily exchange for deuterons in the solvent) were determined and compared to those previously reported by us for AVP in D 2 O at pD 3.8 and 20°C ( Wyssbrod et al., 1979a , b ). Values of δ of corresponding protons in DAVP and AVP are quite similar, and small perturbations in these values for protons in the prolyl-7 and glycyl-9 residues in going from AVP to DAVP can be ascribed to the change in chirality (handedness) at the C α of the adjacent arginyl-8 residue. That the observed perturbations are relatively small (⩽ 0.03 ppm) is probably related to extensive conformational interconversion (averaging) in residues 7-9, which comprise the tail moiety, in both peptides. The conformational states of residues 1-6, which comprise the ring moiety, appear to be, for all practical purposes, identical in both peptides.

Effect of valinomycin on isolated urinary bladder of Pseudemys scripta. I. Effect on electrical parameters under aerobic conditions

Abstract 1. 1. Isolated hemibladders of the fresh-water turtle, Pseudemys scripta , were bathed on both surfaces by oxygenated, Na + -Ringer solution (17 mM HCO 3 − buffer) and were maintained in a short-circulated state. 2. 2. The cyclic dodecadepsipeptide antibiotic, valinomycin, was added to a final concentration of 1 μM to either the mucosal or serosal surface of one hemibladder while the paired hemibladder served as a time control. 3. 3. Addition of valinomycin to the mucosa resulted in a 60 ± 15% increase in total transbladder resistance ( R t ), in a 60 ± 10% decrease in short-circuiting current ( I sc ) and in a 40 ± 10% decrease in spontaneous open-circuited transbladder potential difference (PD oc ) for the valinomycin-treated hemibladders relative to the control hemibladders. 4. 4. Half-maximal effect of valinomycin added to the mucosa was achieved 18 min after addition for I sc ; 24 min for PD oc ; and 30 min for R t . 5. 5. Addition of valinomycin to the serosa did not result in any change in electrical parameters.