N.m.r. and biochemistry

The role and historical progress of n.m.r. applications in biochemistry are briefly outlined. Technical advances over the years have made n.m.r., at last, a technique which can give valuable information about a wide range of biochemical topics, from enzyme kinetics in vivo to the structure of protein-DNA complexes. Emphasis here is placed on studies of proteins, especially those made up from mosaics of modules. It is shown that n.m.r. can readily give detailed structural information about individual protein modules and that valuable information about the structure and function of the intact mosaic protein can be inferred.     

F.t.-i.r. and laser-Raman spectra of thymine and thymidine

F.t.-i.r. and laser-Raman spectra of thymine and thymidine in the solid state were recorded. Assignments were proposed for the frequencies observed. The influence of the deoxy sugar on the vibrations of the nucleoside are discussed as a function of its particular puckering. The aim of this work is to elucidate the differences between the molecules constituting the nucleic acids, in order the better to comprehend their biological functions.     

Turbidity and kelp holdfast amphipoda. I. Wales and S. W. England

Analyses are given of a collection of over 65,000 amphipods derived from kelp holdfasts surveyed around Wales and S.W. England. Faunal affinity is predominantly biased latitudinally, warmwater elements being confined to the extreme southwest. Total amphipod density is related to holdfast weight. There are no significant differences in amphipod density with differences in wave exposure or turbidity. Standardized density is, however, higher in west coast than in east coast holdfasts. Diversity is lower in turbid waters due to the increased dominance of a few species. The distribution, population structure, and fecundity of the previously implicated turbidity-susceptible species, Lembos websteri Bate and Corophium bonnellii Milne Edwards are examined in the light of new ethological information. Supporting and conflicting data are examined and mechanisms are suggested to show how suspended inorganic particles could be directly detrimental to both species. In addition, indirect effects involving climatic fluctuation and competitive interactions, particularly with C. sextonae Crawford emend. Hurley and Jassa falcata (Montagu) cannot be excluded.     

F.t.-i.r. and laser-Raman spectra of cytosine and cytidine

Fourier-transform infrared (F.t.-i.r.) and laser-Raman spectra of cytosine and cytidine in the solid state have been recorded and assignments of the frequencies made. Comparison of the observed frequencies for cytosine with those for cytidine permits identification of the bands characteristic of the sugar on the one hand, and of the pyrimidine base on the other.     

Chimeric twins. T.S. and M.R. reexamined

A pair of chimeric twins, T.S. (male) and M.R. (female), were examined. The amounts of 'foreign' blood cells in each twin found on three occasions were compared. The percentages of M.R. cells found in the blood of T.S. in 1977 and in 1982 were similar and about 1/5 of that found in 1970. The amount of T.S.-blood cells found in M.R. was declining slowly from about 31% in 1970 to about 25% in 1982.     

Iodoglucagon. Preparation and characterization.

Iodinated derivatives of glucagon containing an average of 1 to 5 g-atoms of 127I per mol have been prepared by reacting the hormone with increasing amounts of iodine monochloride. Their iodoamino acid composition has been determined by ion-exchange chromatography and electrophoresis, following hydrolysis by pronase. Iodination of the two tyrosyl residues occurs first and is nearly complete after addition of a 4-fold molar excess of ICl. Iodination of the single histidyl residue is a later event and does not exceed an average of one atom per residue. Hydrolysis of iodoglucagon by trypsin and subsequent separation of the iodotyrosyl peptides shows that iodine is equally distributed between tyrosyl residues 10 and 13. Crude iodoglucagon containing an average of 1 g-atom of iodine per mol has been resolved into several components of differing iodine content and iodoamino acid composition by chromatography on DEAE-cellulose. Monoiodoglucagon isolated by this procedure shows a single band when analyzed by polyacrylamide gel electrophoresis. Iodoglucagons containing an average of 1 to 4 g-atoms of iodine per mol are more potent than native glucagon in their ability to stimulate adenylate cyclase activity and to bind to glucagon receptors of liver cell membranes of the rat. The maximal increase in biological potency occurring upon iodination is about 5-fold with respect to adenylate cyclase activity, and 2-fold with respect to binding to receptors; tetra and triiodinated derivatives show, respectively, the highest potency. Similar effects occur whether inactivation by liver membranes is inhibited or not, indicating an enhancement in the intrinsic affinity of iodoglucagon for the receptors. Iodination beyong 4 g-atoms per mol slightly decreases the affinity of the hormone for adenylate cyclase and for the receptors. Iodination causes a 2-20 fold decrease in the ability of liver plasma membranes and of blood plasma to inactivate glucagon in vitro; these effects correlate with the degree of iodination. With liver microsomal membranes, a decrease in glucagon inactivation occurs only at iodine contents exceeding 4 g-atoms per mol, and lower degrees of iodination result in opposite effects. Monoiodination causes a 4-6-fold increase in the plasma concentration of glucagon within the first 18 min following a single intrvenous injection of the hormone to rats. More extensive iodination results, in addition, in a marked decrease in the rate of dissappearance of glucagon from the blood. The immunological reactivity of glucagon is little affected by monoidination, but strongly depressed by higher degrees of iodination...