Energy uptake in the first step of visual excitation

Perception of light by the retina starts with the absorption of a photon by 11-cis retinal, which is covalently incorporated into the membrane-bound protein, rhodopsin. The initial result of photon capture is the very rapid formation of a red-shifted species, bathorhodopsin (also known as prelumirhodopsin), which is (meta-)stable at liquid nitrogen temperature but which decomposes at higher temperatures, in the dark, through a series of intermediate stages, resulting in the release of all-trans retinal from the apoprotein, opsin. Bathorhodopsin formation is the only photochemical step in the overall reaction and, therefore, merits investigation. Several models for the process have been proposed, and have been critically reviewed, although no consensus yet exists as to the nature or mechanism of formation of the batho intermediate. I report here on the first direct measurement of photon energy uptake during bathorhodopsin formation from bovine rhodopsin, and on its possible significance.     

The determination of the structure of Saturn's F ring by nearby moonlets

Saturn's narrow F ring exhibits several unusual features that vary on timescales of hours to years. These include transient clumps, a central core surrounded by a multistranded structure and a regular series of longitudinal channels associated with Prometheus, one of the ring's two 'shepherding' satellites. Several smaller moonlets and clumps have been detected in the ring's immediate vicinity, and a population of embedded objects has been inferred. Here we report direct evidence of moonlets embedded in the ring's bright core, and show that most of the F ring's morphology results from the continual gravitational and collisional effects of small satellites, often combined with the perturbing effect of Prometheus. The F-ring region is perhaps the only location in the Solar System where large-scale collisional processes are occurring on an almost daily basis.     

Molecular cloning and nucleotide sequence of a transforming gene detected by transfection of chicken B-cell lymphoma DNA

A transforming gene detected by transfection of chicken B-cell lymphoma DNA has been isolated by molecular cloning. It is homologous to a conserved family of sequences present in normal chicken and human DNAs but is not related to transforming genes of acutely transforming retroviruses. The nucleotide sequence of the cloned transforming gene suggests that it encodes a protein that is partially homologous to the amino terminus of transferrin and related proteins although only about one tenth the size of transferrin.     

Vasotocin protects rats against convulsions induced by pentylenetetrazol

Summary The AVP analog, vasotocin, administered s. c. effectively antagonized pentylenetetrazol-induced convulsions, supporting the contention that AVP may be a mediator in convulsive disorders.This work was supported by the Medical Research Council of Canada.     

Structure of porphobilinogen deaminase reveals a flexible multidomain polymerase with a single catalytic site.

The three-domain structure of porphobilinogen deaminase, a key enzyme in the biosynthetic pathway of tetrapyrroles, has been defined by X-ray analysis at 1.9 A resolution. Two of the domains structurally resemble the transferrins and periplasmic binding proteins. The dipyrromethane cofactor is covalently linked to domain 3 but is bound by extensive salt-bridges and hydrogen-bonds within the cleft between domains 1 and 2, at a position corresponding to the binding sites for small-molecule ligands in the analogous proteins. The X-ray structure and results from site-directed mutagenesis provide evidence for a single catalytic site. Interdomain flexibility may aid elongation of the polypyrrole product in the active-site cleft of the enzyme.     

Amino acid concentrations in blood of patients with an acute myocardial infarction

Summary Levels of essential and nonessential amino acids in blood of patients with an acute myocardial infarction (AMI) were found in general not to differ from values obtained from non-AMI patients. This is in contrast to blood taurine levels which are elevated in the AMI patients.