Insect pupil mechanisms

Summary The spectral characteristics of the pupil mechanism in blowfly photoreceptors and their dependence on light intensity have been investigated together with the intensity dependence of the receptor potential. The threshold for the pupil response as measured by reflectance is found at an intensity at which the peak of the receptor potential is about half maximal and the plateau potential starts to saturate. The reflectance saturates at about 3 log-units above threshold. The reflectance spectrum peaks near 620 nm, and its shape is independent of adaptation intensity. The absorbance change, measured by transmission, is extreme in the blue, at about 470 nm. The shape of the absorbance spectrum is slightly intensity dependent, presumably due to optical waveguide effects. The dynamic ranges of the light-induced reflectance and absorbance changes do not coincide. The reflectance change shows saturation at least 1 to 1.5 log units before the absorbance change saturates.     

Effect of aromatic isothiocyanates on the functional properties of human hemoglobin. Role of the stereochemistry of the charged group

The effect of chemical modification of hemoglobin with six derivatives of benzene isothiocyanate has been studied. The negatively charged reagents (isothiocyanates of benzoic and benzenesulfonic acids) markedly inhibit the interaction of hemoglobin with allosteric effectors such as H+, Cl- and organic phosphates; the affinity for heme ligands in the absence of effectors is reduced but cooperativity is maintained, making these modified hemoglobins suitable models for a possible 'blood substitute'. The only uncharged reagent tested (isothiocyanate of benzenesulfonamide) increases the oxygen affinity of hemoglobin and affects only slightly the interaction with heterotropic ligands; its potential use as an antisickling drug is under study.     

Gender differences in anaerobic power tests

The purpose of this study was to determine if the differences in anaerobic power between males and females could be accounted for by differences in body composition, strength, and neuromuscular function. A total of 82 untrained men and 99 women took part in the study. Body composition, somatotype, isometric strength, neuromuscular function were measured, and four anaerobic power tests performed. The men were significantly different from the women on all strength, power, and neuromuscular measurements except reaction time and on all anthropometric and somatotype dimensions except ectomorphy. Strength and anthropometric dimensions were similarly related to anaerobic power values within each sex. Relative fat (%fat) exerted different degrees of influence on sprint and jump performances in each sex. Removing the influence of anthropometric, strength, and neuromuscular differences by analysis of covariance reduced, but did not remove, the significant differences between the sexes. Therefore, factors other than lean body mass, leg strength, and neuromuscular function may be operating in short-term, explosive power performances to account for the differences between the sexes. The task-specific nature of anaerobic power tests and the relatively large influence of anthropometric factors on power production were confirmed.     

Relaxin

1. Relaxin is a hormone of reproduction that appears to affect parturition, uterine accommodation, and sperm motility to varying degrees in many species. 2. All relaxins have the same two chain, disulfide-linked insulin-like structure and two arginine residues in the midregion of the B chain. 3. The active relaxin molecule is produced by excision of a connecting peptide from the prohormone. 4. The biosynthetic pathways of insulin and relaxin are alike, but the relaxin prohormone is about twice as large as the corresponding proinsulin. 5. The primary structures of relaxins from apparently closely related species differ significantly in their amino acid compositions and do not fit into the traditional scheme of molecular evolution.     

Plasmid transformation and replica filter plating of Acholeplasma laidlawii

The restriction deficient mutant 8195 of Acholeplasma laidlawii strain JA1 was transformed by the promiscuous streptococcal plasmid vector pNZ18 at a frequency of 4 x 10(-4)/cfu. The plasmid was maintained without structural rearrangements but was lost in the absence of a selection pressure, i.e. kanamycin or neomycin. Transformed primary colonies were easily recognized due to a different colony morphology. Replica filter plating, previously not obtained with mycoplasmas, was achieved using pNZ18 as a marker by incubating the replica filters with the cell side down on the new agar plates. These findings should greatly facilitate the genetic and functional analysis of A. laidlawii.     

Conformation of a cyclic decapeptide analog of a repeat pentapeptide sequence of elastin: cyclo-bis(valyl-prolyl-alanyl-valyl-glycyl)

The conformation of a cyclic decapeptide analog of a repeat sequence of elastin has been determined in the crystalline state using X-ray crystallographic techniques. Tetragonal crystals were grown from a solution of the decapeptide in water; space group P4(2)2(1)2, a = 19.439(2) & c = 13.602(1) A, with four formula units (C40H66N10O10.4H2O) per unit cell. The cyclic decapeptide in the crystal exhibits exact twofold symmetry. The asymmetric unit contains one pentapeptide and two water molecules for a total of 32 nonhydrogen atoms. The structure has been determined by the application of direct methods and refined by full-matrix least squares to an R index of 0.053 for 2272 reflections with intensities greater than 2 sigma(I). The backbone conformation of the asymmetric pentapeptide can be described as consisting of a double beta bend of Type III-I. The Type III turn has Pro (phi = -59.3 degrees, psi = -26.8 degrees) and Ala (phi = -65.9 degrees, psi = -23.1 degrees) at the corners while Type I turn has Ala (phi = -65.9 degrees, psi = -23.1 degrees) and Val (phi = -98.9 degrees, psi = 8.3 degrees) as the corner residues. The cyclic decapeptide has two such double bends linked together by Gly-Val bridges.