Nitrogen-15 nuclear magnetic resonance of aliphatic tripeptides

The 15N chemical shifts of eight aliphatic tripeptides have been measured at the natural-abundance level. For a given tripeptide, the resonances of the COOH-terminal and NH2-terminal amino acids can be identified by measurements at low or high pH. The shifts of the NH2-terminal amino acid nitrogens are essentially independent of the amino acids in the rest of the peptide. The shifts of the other nitrogens are characteristic of the amino acids themselves and of the immediately preceding amino acid toward the NH2 terminus. Non-terminal amide nitrogens have shifts of about 6 ppm upfield of COOH-terminal amide nitrogens at the isoelectric point of measurement. 15N chemical shifts appear to have considerable potential value for peptide sequencing.

Mode of action of trichloroethylene on squid axon membranes

The mode of action of trichloroethylene on electrical properties of squid giant axons has been studied by means of voltage clamp techniques. Trichloroethylene decreased the resting membrane potential in a manner dependent upon the concentration, the depolarization by 50% saturated trichloroethylene attaining 28.4 and 32.7% of the initial value at 20 and 10 degrees C, respectively. Leakage conductance was decreased to 34.6% of the control by 30% saturated trichloroethylene at 10-12 degrees C. It appears that the trichloroethylene-induced depolarization is at least in part due to a decrease in resting potassium permeability. Both peak transient and steady-state conductance increases were suppressec by trichloroethylene, and the curve relating the steady-state conductance to the membrane potential was shifted in the depolarizing direction while the peak transient conductance curve was not appreciably shifted. The reversal potential for the peak transient current was greatly shifted by trichloroethylene in the direction of hyperpolarization in a manner dependent on the concentration, the maximum shift amounting to 25 mV at 10 degrees C. This effect was less pronounced at 20 degrees C. The shift in the reversal potential is mostly due to a decrease in selectivity of the peak transient channel and partly due to an accumulation of sodium ions inside. Analyes of dose-response relation in suppressing peak transient and steady-state conductances show that trichloroethylene interacts with receptor on a one-to-one stoichiometric basis. Steady-state sodium inactivation curve was shifted by trichloroethylene in the direction of hyperpolarization. All of these effects were partially reversed after washing the axon with anesthetic-free media. The accumulation of sodium ions inside would be much more pronounced in small nerve fibers in the brain than in giant axon and, together with the observed decrease in the selectivity of peak transient channels, would play a significant role in general anesthesia.

Excess occurrence of cancer of the oral cavity, lung, and bladder following cancer of the cervix

The risk of developing a second cancer among white and black females with an initial cancer of the uterine cervix or corpus has been estimated based on the experience of the Charity Hospital of Louisiana Tumor Registry, a participant of the End Results Program of the National Cancer Institute. Observed second primary cancers were compared to expected numbers in order to obtain a direct estimate of risk. White females having an initial cancer of the cervix had a 5-to-6-fold excess risk of developing a subsequent cancer of the oral pharynx, lung or bladder during the first 5 years following their initial cancer with no excess risk for developing subsequent cancer of the breast or large intestine, but a slight excess risk for developing subsequent cancer of the ano-rectum. There was a 7% excess risk among both whites and blacks with initial cancer of the corpus uteri of subsequently developing another cancer.

Applications of natural-abundance nitrogen-15 nuclear magnetic resonance to large biochemically important molecules

Natural-abundance nitrogen-15 nuclear magnetic resonance spectroscopy of enzymes and other biopolymers is found to be feasible using newly available instrumentation. The long correlation times of such molecules result in short spin-lattice relaxation times, and these in turn allow rapid signal accumulation. The advantages of short T1 values are sometimes offset, however, by unfavorable nuclear Overhauser effects. The dependence of T1 and nuclear Overhauser effects upon correlation time is discussed, and preliminary nitrogen-15 nuclear magnetic resonance results for several biopolymers, including lysozyme, protamines, pepsin, hemoglobin, vitamin B 12, and tRNA, are presented.

Nuclear magnetic resonance spectroscopy: reinvestigation of carbon-13 spin-lattice relaxation time measurements of amino acids

The carbon-13 spin-lattice relaxation times (T1) of glycine have been measured as a function of pD and concentration. Contrary to previously reported findings, no significant dependence was observed on either pD or concentration. In addition, the T1 values reported here are much longer than those published earlier. The discrepancies arise from the presence of paramagnetic impurities in the earlier samples. For the carboxyl carbon, dipole-dipole relaxation is dominant in both D2O and H2O solution, and in H2O there is a significant intermolecular dipolar contribution. Proton and oxygen relaxation times have also been measured. These, along with the carbon relaxation data, allow a discussion of the dynamics of glycine in solution.

Multiple primary neoplasms in blacks compared to whites. IV. Further cancers in patients with cancer of the digestive organs

Second primary cancers found among whites and blacks with initial cancer of the digestive organs were reported based on data from the Charity Hospital Tumor Registry. Observed second primary cancers were compared to expected numbers to obtain a direct estimate of risk. Both white and black men had about a twofold risk of developing a second cancer. For white men, the excess was limited to a subsequent skin cancer, but this finding was probably an artifact of reporting and lacked biologic significance. Among women, both white and black, large excesses of invasive cancer of the cervix and ovary were found after an initial cancer of the large intestine and anorectum was discovered. No excess of breast cancer was found.

Acoustic analysis of an intergrade zone between two call races of the Limnodynastes tasmaniensis complex (Anura : Leptodactylidae) in south-eastern Australia

Mating calls of the northern and southern call races of the L. tasmaniensis complex are described. Analysis of call structure along a transect across the main contact between these allopatric forms in north central Victoria indicates that there is a zone of intergradation between 90 and 135 km wide, about 215 km long and with a north-westerly orientation. The interaction is interpreted as a secondary contact in which there is hybrid or recombinant superiority along a subtle ecological gradient.

Carbon-13 nuclear magnetic resonance spectroscopy. Structure of the anticoagulant warfarin and related compounds in solution

Carbon-13 nuclear magnetic resonance spectra have been obtained for the coumarin-related compounds warfarin and phenprocoumon. The spectral assignments indicate that warfarin exists as a mixture of cyclic hemiketal diastereomers in dimethyl sulfoxide solution. The sodium salt of warfarin exists as the ringopen form in water solution.

Nuclear magnetic resonance spectroscopy. Carbon-13 spin-lattice relaxation time measurements of amino acids

The (13)C spin-lattice relaxation times, T(1)'s, of several amino acids have been measured as a function of pD and concentration. A strong dependence of the carboxyl carbon T(1) was observed for both pD and concentration and is believed to be due to intermolecular associations. For the carboxyl carbon, spin rotation is proposed as the predominant relaxation mechanism, whereas the other carbons are relaxed mainly by the dipole-dipole mechanism, and their relaxation times are relatively independent of changes in concentration and pD.