The subunit structure of rat liver pyruvate kinase

The amino acid composition for rat liver pyruvate kinase is reported. Thin layer peptide mapping of the tryptic digests yields 44 ninhydrin-reactive peptides, which is one-quarter the total number of lysyl and arginyl residues. No amino-terminal residue has been detected using the dansyl chloride procedure. Acid urea disc gel electrophoresis of the protein subunits yields only one protein band; yet, isoelectric focusing of the subunits in urea yields two protein bands. These results suggest that pyruvate kinase (L-type isozyme) consists of four subunits of similar primary structure, but with sufficient microheterogeniety to be able to resolve two types of subunits upon isoelectric focusing.     

Re-mapping Robert Rosen's (M,R)-systems

The central concern of this paper is to re-evaluate Rosen's replicating (M,R)-systems, presented in his book 'Life Itself ', where M and R signify metabolism and repair, respectively. We look anew at Rosen's model of an organism in the light of extensive research into natural hierarchical systems, and the paper presents conclusions drawn from a comparison between Rosen's relational model and that of a birational complementary natural hierarchy. We accept that Rosen's relational model provides a useful stepping stone to understanding the nature of life, but also suggest that it induces potentially digressive conclusions. We conclude that a binary segregation of relational assemblies into mechanisms and organisms is insufficient, and indicate how a threefold segregation throws new light on Rosen's model. An organism is not 'the complement of a mechanism': the complement of a mechanism is its ecosystem. An organism is the 'complex interface' between mechanism and ecosystem.     

695. SALVIA CAYMANENSIS

Originally described by Charles Frederick Millspaugh in 1900, Salvia caymanensis Millsp. & Uline, the cayman sage , is known only from Grand Cayman, a Caribbean UK Overseas Territory; it was thought extinct in the wild until its rediscovery in 2007. Although the species is secure ex situ, its in situ future remains uncertain and it has been red listed as critically endangered. S. caymanensis is illustrated, its botanical history described and conservation measures discussed.     

Pesticide exposure: the hormonal function of the female reproductive system disrupted?

Some pesticides may interfere with the female hormonal function, which may lead to negative effects on the reproductive system through disruption of the hormonal balance necessary for proper functioning. Previous studies primarily focused on interference with the estrogen and/or androgen receptor, but the hormonal function may be disrupted in many more ways through pesticide exposure. The aim of this review is to give an overview of the various ways in which pesticides may disrupt the hormonal function of the female reproductive system and in particular the ovarian cycle. Disruption can occur in all stages of hormonal regulation: 1. hormone synthesis; 2. hormone release and storage; 3. hormone transport and clearance; 4. hormone receptor recognition and binding; 5. hormone postreceptor activation; 6. the thyroid function; and 7. the central nervous system. These mechanisms are described for effects of pesticide exposure in vitro and on experimental animals in vivo. For the latter, potential effects of endocrine disrupting pesticides on the female reproductive system, i.e. modulation of hormone concentrations, ovarian cycle irregularities, and impaired fertility, are also reviewed. In epidemiological studies, exposure to pesticides has been associated with menstrual cycle disturbances, reduced fertility, prolonged time-to-pregnancy, spontaneous abortion, stillbirths, and developmental defects, which may or may not be due to disruption of the female hormonal function. Because pesticides comprise a large number of distinct substances with dissimilar structures and diverse toxicity, it is most likely that several of the above-mentioned mechanisms are involved in the pathophysiological pathways explaining the role of pesticide exposure in ovarian cycle disturbances, ultimately leading to fertility problems and other reproductive effects. In future research, information on the ways in which pesticides may disrupt the hormonal function as described in this review, can be used to generate specific hypotheses for studies on the effects of pesticides on the ovarian cycle, both in toxicological and epidemiological settings.     

Phylogeny of the Drosophila saltans species group based on combined analysis of nuclear and mitochondrial DNA sequences

Nucleotide sequences from two nuclear loci, alcohol dehydrogenase and internal transcribed spacer-1 of the nuclear ribosomal DNA repeats, and two mitochondrial genes, cytochrome oxidase I and cytochrome oxidase II, were determined from nine species in the Drosophila saltans species group. The partition homogeneity test and partitioned Bremer support were used to measure incongruence between phylogenetic hypotheses generated from individual partitions. Individual loci were generally congruent with each other and consistent with the previously proposed morphological hypothesis, although they differed in level of resolution. Since extreme conflict between partitions did not exist, the data were combined and analyzed simultaneously. The total evidence method gave a more resolved and highly supported phylogeny, as indicated by bootstrap proportions and decay indices, than did any of the individual analyses. The cordata and elliptica subgroups, considered to have diverged early in the history of the D. saltans group, were sister taxa to the remainder of the saltans group. The sturtevanti subgroup, represented by D. milleri and D. sturtevanti, occupies an intermediate position in this phylogeny. The saltans and parasaltans subgroups are sister clades and occupy the most recently derived portion of the phylogeny. As with previous morphological studies, phylogenetic relationships within the saltans subgroup were not satisfactorily resolved by the molecular data.      

Phylogenetic analysis supports horizontal transfer of P transposable elements

Nucleotide sequence comparisons were used to investigate the evolution of P transposable elements and the possibility that horizontal transfer has played a role in their occurrence in natural populations of Drosophila and other Diptera. The phylogeny of P elements was examined using published sequences from eight dipteran taxa and a new, partial sequence from Scaptomyza elmoi. The results from a number of different analyses are highly consistent and reveal a P-element phylogeny that contradicts the phylogeny of the species. At least three instances of horizontal transfer are necessary to explain this incongruence, but other explanations cannot be ruled out at this time.      

Glycosylation of LDL decreases its ability to interact with high-affinity receptors of human fibroblasts in vitro and decreases its clearance from rabbit plasma in vivo

Incubation of human LDL in vitro at 37 degrees C for 48 h with [14C]glucose at concentrations from 5 to 200 mM resulted in a glycosylated LDL, containing 0.4-20 mol of glucose incorporated per apolipoprotein B of 250 000 daltons. The extent of glucose incorporated was proportional to the time of incubation and concentration of glucose. Glycosylation of LDL abolished its uptake and degradation by the high-affinity process for LDL in normal human skin fibroblasts. 125I-labeled glycosylated LDL was bound, internalized and degraded by the fibroblasts via a nonspecific low-affinity process. The 125I-labeled glycosylated LDL and 125I-labeled LDL were taken up and degraded at similar rates in a non-saturable, low-affinity process by peritoneal macrophages isolated from mice. When 125I-labeled glycosylated LDL or 125I-labeled LDL were injected into rabbits, the glycosylated LDL had a delayed plasma clearance in comparison to the LDL. The mean fractional catabolic rates were 0.67 day-1 and 1.70 day-1 for 125I-labeled glycosylated LDL and 125I-labeled LDL, respectively. The uptake and degradation of 125I-labeled LDL by human skin fibroblasts was decreased as the concentration of free carbohydrate, glucose, sucrose or sorbitol, in the medium was increased from 10 mM to 1 M. It is speculated that pathologic levels of plasma glucose in vivo could result in a decrease in LDL uptake as a result of glycosylation of LDL. A decrease in uptake of native or modified LDL in vivo could contribute to hypercholesterolemia and its pathophysiology.     

Glycosylation of human LDL and its metabolism in human skin fibroblasts

Extrachromosomal DNA of heterogeneous size has been isolated from bursal lymphocytes and splenocytes of five week old chickens, and from splenocytes of mice. This DNA contains covalently closed circles, open circles, and open circles with tails. Open circular molecules with and without tails are more frequent than covalently closed species, and the total number of small circular DNA molecules per cell is in the range of 100–200 copies.     

Nonenzymatic galactosylation of human LDL decreases its metabolism by human skin fibroblasts

Incubation of human LDL with galactose in vitro resulted in a glycosylated-LDL containing radiolabel covalently attached to apo B. The rate of radiolabel incorporation was proportional to the time of incubation and concentration of carbohydrate. The rate of incorporation of galactose into apo B was higher than with glucose or mannose. The nonenzymatic glycosylation of LDL decreased its uptake and metabolism by the high affinity, receptor dependent process for LDL in normal human skin fibroblasts.