Depalmitylation with hydroxylamine alters the functional properties of rhodopsin

Rhodopsin, the photosensitive protein found in rod photoreceptors, has two covalently attached palmitates that are thought to anchor a portion of the C terminus to the disc membrane, forming a fourth cytoplasmic loop. Using hydroxylamine (NH2OH) to cleave the thioester linkage, we have characterized the effect of depalmitylation on certain functional properties of rhodopsin. Treatment of rod outer segment membranes (prepared from rat retinas previously labeled in vivo with [3H]palmitate) with 1 M NH2OH typically removed greater than or equal to 75% of the [3H]palmitate initially bound to rhodopsin. Spectrophotometry of rod outer segment membranes that had been treated with 1 M NH2OH indicated preservation of 85% of the native rhodopsin and no effect on the shape of the absorbance spectrum of rhodopsin. In vivo labeled rhodopsin that had been treated with 1 M NH2OH did not reincorporate free endogenous [3H] palmitate over a 2-h incubation period. Both NH2OH-treated and untreated rhodopsin incorporated [14C]palmitate from exogenously added [14C]palmitoyl-CoA. This incorporation was substantially greater in the NH2OH-treated sample. The removal of palmitate by NH2OH inhibited rhodopsin regeneration by 44% and increased the ability of rhodopsin to activate transducin's light-dependent GTPase activity by 61%. However, the removal of palmitate from rhodopsin did not affect the light-dependent binding of transducin (T alpha and T beta gamma).     

Molecular mapping of the mouse ob mutation.

The mouse ob mutation has been mapped relative to a series of RFLPs among the progeny of three separate mouse crosses: an intraspecific backcross, an intraspecific intercross, and an interspecific intercross. Genotypic assignment at the ob locus was made by making use of measurements of body mass index and the plasma concentrations of glucose and insulin. These data have suggested that the development of diabetes in these animals is a consequence of unlinked polygenes. There was also evidence that unlinked Mus spretus alleles can diminish the obesity of ob/ob mice. From these data we have mapped several markers on chromosome 6 with the following order: cen-Cola-2-Met-ob-Cpa-Tcrb. The homologs of markers that flank ob map to human chromosome 7q, suggesting that if there is a human homologue of ob, it maps to 7q31.     

The reproductive behavior of six species of Namib desert tenebrionid beetles (Coleoptera: Tenebrionidae)

The reproductive behavior of six species of tenebrionid beetles (Coleoptera: Tenebrionidae) was studied in the Namib Desert of southern Africa. In three species, males follow closely behind females (following behavior), while in the other three species, males mount females and remain clasped to them for extended periods (riding behavior). Following behavior occurs before and sometimes after copulation, while riding behavior occurs primarily after copulation. Males of all six species guard females from contesting males, although the effectiveness of guarding is greater in riding species. The evolution of the two male mating strategies does not appear to be related to operational sex ratio differences but, rather, to differential tendencies of females to remate. Variation in total pair duration within following and riding species may be attributed partly to species differences in operational sex ratio. However, pair durations are not affected by experimental manipulations of sex ratio in each species.     

Phylogenetic relationships among four members of Stizostedion (Percidae) determined by mitochondrial DNA and allozyme analyses

Phylogenetic relationships among four Stizostedion species were examined using mitochondrial DNA (mtDNA) and allozyme analyses. Twenty-six allozyme loci were scored, and mtDNA variation was examined using 24 restriction endonucleases, yielding 48–57 restriction sites among the species. Genetic distance analyses show that the two North American species ( S. canadense and S. vitreum ) cluster in one group, while the two European species ( S. hciopercu and S. vogense ) form a second group. Nei's genetic distance between these two groups was 0.7 ± 0.2 for allozymes, while the corresponding mtDNA sequence divergence was 14.8 ± 2.0%, suggesting that these two groups diverged approximately 10 million years ago. Thus, these data are consistent with the hypothesis that Stizostedion colonized North America during the Pliocene.     

Structure and biological activity of crustacean gastrointestinal peptides identified with antibodies to gastrin/cholecystokinin.

Four gastrin/cholecystokinin-like peptides (G/CCK) which cross-react with a specific C-terminal gastrin/CCK antiserum have been isolated from the stomach of the marine crustacean Nephrops norvegicus. The molecular weight of the four peptides was estimated between 1000 and 2000 Da by molecular sieving. By radioimmunoassay, the cross-reactivity of these peptides with human gastrin 17-I was found to be around 0.03%. Pure peptidic fractions were recovered after four successive steps of HPLC. Amino-acid analysis suggested a similarity between the four peptides identified which may belong to a new family. A limited homology between the C-terminus of one Nephrops peptide and vertebrate G/CCK was found after sequencing. Two of the peptides exhibited secretagogue effects on crustacean isolated midgut glands. The Nephrops peptides, although structurally distinct from the vertebrate G/CCKs, appear to serve similar biological functions in crustaceans.     

Induction of DNA bending by bifunctional intercalating agents of the 7H-pyridocarbazole family

The structures and binding energetics of selected complexes formed between the deoxynucleotides d(CpGpGpCpG).d(CpGpCpCpG), d(CpGpApTpCpG)2, d(GpCpGpCpCpG).d(CpGpGpCpGpC), and d(CpGpCpCpCpG)2 with the DNA bifunctional intercalating agent ditercalinium and three of its rigid linking chain derivatives have been investigated theoretically by means of a molecular mechanics approach that takes into account nucleic acid flexibility, ligand flexibility and solvent dielectric effects (R. Lavery, in: Unusual DNA structures, eds S. Harvey and R. Wells (Pergamon, New York, 1988) p. 189; R. Lavery, in: DNA bending and curvature, eds W.K. Olson et al. (Adenine Press, New York, 1988) p. 191). The piperidinium chains of the bis-intercalating ligands are always located in the major groove of DNA. For the energy-minimized complexes the ligand proceeds to bind following preferentially the 5'-pyrimidine-purine-3' alternating sequence, thus dictating the number of internal exclusion sites. The complexes with three exclusion sites will present (i) a bending of the structure towards the major groove, and (ii) a non-ideal distribution of unwinding angles; complexes with less than three exclusion sites will remain essentially linear. The absence of a bend does not preclude other types of local deformations of the base-pairs such as inclination, buckle and tip. The proposed structures of the d(CpGpApTpCpG)2 complexes are in agreement with NMR structural results. The possible relevance of these findings to a previously proposed mode of interaction for ditercalinium-like DNA ligands is discussed.