Vasoactive intestinal peptide regulates cholesterol side-chain cleavage cytochrome P-450 (P-450scc) gene expression in granulosa cells from immature rat ovaries

Vasoactive intestinal peptide (VIP), a neuropeptide present in ovarian nerves, has been previously shown to induce synthesis of the side-chain cleavage cytochrome P-450 enzyme which catalyzes the conversion of cholesterol to pregnenolone (the rate-limiting step in progesterone synthesis). In the present study we demonstrate, by means of a bovine 3'-specific P-450scc cDNA probe, that this VIP effect is exerted at least partially at the level of gene expression in cultured granulosa cells that were isolated from estrogen-primed, immature rats. The size and level of the 2.0 kilobase P-450scc mRNA species was assessed by Northern blot analysis, while the translatability of this mRNA was assayed by immunoisolation of the 35S-labeled P-450scc precursor protein translated from total RNA of control and stimulated granulosa cells. FSH was much more effective than VIP at increasing P-450scc mRNA concentrations in cultured granulosa cells, whereas secretin treatment was ineffective. The results suggest that, like FSH, the stimulatory effect of the neuropeptide VIP on ovarian progesterone secretion involves regulation of P-450scc gene expression during functional maturation of the prepubertal ovary.     

Membrane fluidity of microsomal and thymocyte membranes after X-ray and UV irradiation

A brief literature review shows that ionizing radiation in biological membranes and in pure lipid membranes causes malondialdehyde formation, indicating lipid peroxidation processes. With respect to membrane fluidization by ionizing radiation, in pure lipid membranes rigidization effects are always reported, whereas contradictory results exist for biological membranes. Starting from the assumption that membrane proteins at least partly compensate for radiation effects leading to a rigidization of membrane lipid regions, pig liver microsomes, as a representative protein-rich intracellular membrane system, were irradiated with X-rays or UV-C with doses up to 120 Gy at a dose rate of 0.67 Gy min^–1 and up to 0.73 J cm^–2 at an exposure rate of 16.2 mJ cm^–2 min^–1, respectively. For both irradiation types a weak but significant positive correlation between malondialdehyde formation and membrane fluidity is revealed throughout the applied dose ranges. We conclude that the membraneous protein lipid interface increases its fluidity under radiation conditions. Also, thymocyte ghosts showed an increased fluidity after X-ray irradiation. Fluidity measurements were performed by the pyrene excimer method.     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.      

Fructose 1,6-bisphosphatase: Dissociation of AMP cooperativity and AMP inhibition by carbamylation

Selective treatment of pig kidney fructose 1,6-bisphosphatase with potassium cyanate leads to the formation of an active carbamylated enzyme that has lost the cooperative interactions among AMP sites, but retains sensitivity to inhibition of catalytic activity by the regulator AMP. Incorporation data on [¹⁴C]KNCO indicate that the loss of enzyme cooperativity at the AMP sites is related to selective carbamylation of four lysine residues per mole of tetrameric enzyme. Exhaustive carbamylation suggests that a second lysine residue per subunit is essential for AMP inhibition.     

An A alpha Ser-434 to N-glycosylated Asn substitution in a dysfibrinogen, fibrinogen Caracas II, characterized by impaired fibrin gel formation.

We have identified a unique N-glycosylated Asn substitution for a Ser at position 434 of the A alpha chain of an abnormal fibrinogen designated fibrinogen Caracas II. This dysfibrinogen was characterized by impaired fibrin monomer aggregation. Since there were 4 Thr residues immediately following the mutation, a new Asn-X-Thr/Ser-type consensus sequence, Asn-Thr-Thr arose for N-glycosylation of the Asn. The extra oligosaccharide was found to consist mainly of a disialylated biantennary structure comprising 81.9%, while a neutral and a monosialylated biantennary oligosaccharide represented only 3.6% and 14.5%, respectively. The mutation resides in the carboxyl-terminal region of the A alpha chain, which could fold back to form an extra small globular region located near the central region of the molecule (Erickson, H.P., and Fowler, W.E. (1983) Ann. N. Y. Acad. Sci. 408, 146-163; Weisel, H.P., Stauffacher, C.V., Bullitt, E., and Cohen, C. (1985) Science 230, 3124-3133). Therefore, the participation of this region, referred to as an additional central domain or an alpha domain, in fibrin gel formation is strongly implicated.