Methane Monooxygenase Biotransformations: Highly Stereoselective Hydroxylation of 3-Methylcyclohexene by Methane Monooxygenase: Steric and Electronic Effects on Product Distribution

Cell extracts containing soluble methane monooxygenase from Methylococcus capsulatus, Methylosinus sporium and Methylosinus trichosporium converted 3-methylcyclohexene to predominantly cis-4-methylcyclohex-2-enol, contrary to an earlier suggestion of rearrangement products. In the case of M. capsulatus extracts, this comprised 90% of the total products. The product mixture was consistent with predictions based on chemical reactivity of the substrate, steric effects in the substrate and products and enzymic constraints operating in concert.     

Assembly rules of ground-foraging ant assemblages are contingent on disturbance, habitat and spatial scale

Aim A major endeavour of community ecology is documenting non‐random patterns in the composition and body size of coexisting species, and inferring the processes, or assembly rules, that may have given rise to the observed patterns. Such assembly rules include species sorting resulting from interspecific competition, aggregation at patchily distributed resources, and co‐evolutionary dynamics. However, for any given taxon, relatively little is known about how these patterns and processes change through time and vary with habitat type, disturbance history, and spatial scale. Here, we tested for non‐random patterns of species co‐occurrence and body size in assemblages of ground‐foraging ants and asked whether those patterns varied with habitat type, disturbance history, and spatial scale. Location Burned and unburned forests and fens in the Siskiyou Mountains of southern Oregon and northern California, USA. Methods We describe ground‐foraging ant assemblages sampled over two years in two discrete habitat types, namely Darlingtonia fens and upland forests. Half of these sites had been subject to a large‐scale, discrete disturbance – a major fire – in the year prior to our first sample. We used null model analyses to compare observed species co‐occurrence patterns and body‐size distributions in these assemblages with randomly generated assemblages unstructured by competition both within (i.e. at a local spatial scale) and among (i.e. at a regional scale) sites. Results At local spatial scales, species co‐occurrence patterns and body‐size ratios did not differ from randomness. At regional scales, co‐occurrence patterns were random or aggregated, and there was evidence for constant body‐size ratios of forest ants. Although these patterns varied between habitats and years, they did not differ between burned and unburned sites. Main conclusions Our results suggest that the operation of assembly rules depends on spatial scale and habitat type, but that it was not affected by disturbance history from fire.     

Men in committed, romantic relationships have lower testosterone

Variation in human male testosterone levels may reflect, and effect, differential behavioral allocation to mating and parenting effort. This proposition leads to the hypothesis that, among North American men, those involved in committed, romantic relationships will have lower testosterone levels than men not involved in such relationships. Our study is the first to examine whether being in such a relationship (rather than being married) is the meaningful predictor of male testosterone levels. To test this hypothesis, 122 male Harvard Business School students filled out a questionnaire and collected one saliva sample (from which testosterone level was measured). Results revealed that men in committed, romantic relationships had 21% lower testosterone levels than men not involved in such relationships. Furthermore, the testosterone levels of married men and unmarried men who were involved in committed, romantic relationships did not differ, suggesting that, at least for this sample, male pair bonding status is the more significant predictor of testosterone levels than is marital status.     

Task-specific impairments and enhancements induced by magnetic stimulation of human visual area V5.

Transcranial magnetic stimulation (TMS) can be used to simulate the effects of highly circumscribed brain damage permanently present in some neuropsychological patients, by reversibly disrupting the normal functioning of the cortical area to which it is applied. By using TMS we attempted to recreate deficits similar to those reported in a motion-blind patient and to assess the specificity of deficits when TMS is applied over human area V5. We used six visual search tasks and showed that subjects were impaired in a motion but not a form ''pop-out'' task when TMS was applied over V5. When motion was present, but irrelevant, or when attention to colour and form were required, TMS applied to V5 enhanced performance. When attention to motion was required in a motion-form conjunction search task, irrespective of whether the target was moving or stationary, TMS disrupted performance. These data suggest that attention to different visual attributes involves mutual inhibition between different extrastriate visual areas.     

Dissociation between rate of hepatic lipoprotein secretion and hepatocyte microtubule content

The fact that colchicines inhibits hepatic secretion of very low density lipoprotein (VLDL) particles has been interpreted to mean that microtubules are involved in hepatic VLDL secretion. To further define this relationship, we have attempted to see if changes in hepatic VLDL secretion are associated with changes in hepatocyte microtubule or tubulin content. Accordingly, hepatic secretion of VLDL was increased in rats, and the hepatocyte content of both microtubules (using quantitative morphometric methods) and tubulin (using a time-decay colchicine binding assay) was determined. In acute experiments, VLDL secretion was increased by perfusion of isolated rat livers for 2 h with varying concentrations of free fatty acids (FFA). Results indicate that hepatic VLDL triglyceride (TG) secretion at perfusate FFA levels of 0.7 μEq/ml is threefold greater (P < 0.01) than when livers are perfused without added FFA. However, no differences are observed in the content of microtubules in these livers: specifically, microtubules occupy 0.029 percent of hepatocyte cytoplasm in livers perfused without FFA and 0.030 percent of cytoplasm in livers perfused with FFA. In chronic experiments, rats were fed for 1 wk with either standard rat chow or a hyperlipidemic (sucrose/lard) diet. With the experimental diet, plasma triglyceride levels increase threefold over controls, and liver VLDL-TG production, as determined by [(3)H]glycerol turnover studies, is 55 percent greater (P < 0.01) than controls. However, microtubules occupy 0.027 percent of the cytoplasm of hepatocyte cytoplasm whether rats are on standard or hyperlipidemic diets. Furthermore, the tubulin content of isolated hepatocytes does change, and represents 1 percent of hepatocyte soluble protein, irrespective of diet. These results suggest that increases in hepatic VLDL secretion can occur without any demonstrable change in hepatocyte assembled microtubule or tubulin content, and raise questions as to the role played by microtubules in hepatic VLDL secretion.     

Isolation and characterization of a yeast artificial chromosome (YAC) contig around the human steroid sulfatase gene.

The region surrounding the steroid sulfatase (STS) locus on Xp22.3 is of particular interest since it represents a deletion hot spot, shares homology with the proximal long arm of the Y chromosome (Yq11.2), and contains genes for several well-described X-linked disorders. Here we describe yeast artificial chromosomes (YACs) covering 450 kb around the STS gene. Eight YAC clones were isolated from a human YAC library. Their STS exon content was determined and the overlap of the clones characterized. Two of the YAC clones were found to contain the entire STS gene. The most proximal and the most distal ends of the YAC contig were cloned but neither of them crossed the breakpoints in any of the previously described patients with entire STS gene deletions. This is consistent with deletions larger than 500 kb in all these patients. One of the YAC clones was found to contain sequences from the STS pseudogene on Yq11.2. Two anonymous DNA sequences, GMGXY19 and GMGXY3, previously mapped in the vicinity of the STS locus, were found within the YAC contig and their assignment with respect to the STS locus was thus possible. This contig is useful for the overlap cloning of the Xp22.3 region and for reverse genetic strategies for the isolation of disease genes in the region. Furthermore, it may provide insight into the molecular mechanisms of deletion and translocation events on Xp22.3 and in the evolution of sex chromosomes.     

EFFECTS OF PLANT MORPHOLOGY AND EMERGENCE TIME ON SIZE HIERARCHY FORMATION IN EXPERIMENTAL POPULATIONS OF TWO VARIETIES OF CULTIVATED PEAS (PISUM SATIVUM)

The effects of plant form and emergence time on size hierarchy formation in populations of two morphologically and genetically distinct varieties of peas (leafless and leafed) were studied. There were no significant differences in germinability between the two varieties, although leafless peas imbibed more rapidly than the leafed ones did. Monocultures of leafed and leafless peas were established at two densities: plants grown alone in small pots and plants grown at 576 m -. Time emergence was noted, and plant shape, biomass and seed production were measured at two-week intervals for ten weeks. Seedlings emerged continually over an eight-day period, and two cohorts of seedlings were distinguished (seedlings emerging 6–7 days after planting, and seedlings emerging > 7 days after planting). Dominance and suppression were observed in the high-density populations, and early-emerging plants had less hierarchical biomass distributions than did late-emerging ones. Although leafless peas were larger and suffered less mortality than leafed ones did at identical densities, there were no differences in the degree of size inequality between the two genotypes (emergence cohorts pooled), or within emergence cohorts between genotypes. The degree of size inequality increased with time among dominant individuals and decreased with time among suppressed individuals. These results broadly support Weiner and Thomas's (1986) hypothesis that plant form may affect the extent but not the existence of competitive asymmetry in plant populations.     

The ecology of birth seasonality among agriculturalists in central Africa.

The Lese are subsistence farmers living in the Ituri Forest of north-east Za?re. They exhibit significant birth seasonality, with lowest frequencies of conception when food production is least, nutritional status is low and ovarian function, as measured by salivary steroid hormone levels, is reduced. Efe pygmy foragers, who live in the same geographical area but are less dependent on cultivated foods and have a more flexible life style, do not exhibit frequent fluctuations in nutritional status nor significant birth seasonality. These findings support a model of birth seasonality relating climatic variables to variation in fertility through a causal chain linking rainfall to food production to energy balance to ovarian function to fertility. The model, which emphasises an ecological approach to the study of human reproduction, should have broad applicability since seasonality of food production and energy balance is widespread geographically and across a wide variety of economies and cultures.     

Human male pair bonding and testosterone

Previous research in North America has supported the view that male involvement in committed, romantic relationships is associated with lower testosterone (T) levels. Here, we test the prediction that undergraduate men involved in committed, romantic relationships (paired) will have lower T levels than men not involved in such relationships (unpaired). Further, we also test whether these differences are more apparent in samples collected later, rather than earlier, in the day. For this study, 107 undergraduate men filled out a questionnaire and collected one saliva sample (from which a subject’s T level was measured) at various times across the day. As in previous studies, men involved in committed, romantic relationships had lower salivary T levels, though only during later times of the day. Furthermore, additional analysis of the variation among unpaired subjects indicated that men without prior relationship experience had lower T levels than experienced men. Finally, while paired men as a group had lower T levels than unpaired men, those men at the earliest stage (less than six months) of a current relationship had higher T levels than unpaired men as well as men in longer-term relationships. These results suggest that variation in male testosterone levels may reflect differential behavioral allocation to mating effort. Peter Gray recently completed his Ph.D. in biological anthropology at Harvard with a dissertation entitled, "Human Male Reproductive Strategies: Cross-Cultural and Endocrine Aspects." He is now a postdoctoral fellow at Charles Drew University of Medicine and Science, working with Dr. Shalender Bhasin on human androgen research. Judith Flynn Chapman and Matthew McIntyre are Ph.D. candidates inbiological anthropology at Harvard University. Judith Flynn Chapman focuses on variation in human ovarian function. Matthew McIntyre studies the role of testosterone in psychological development. Terry Burnham is an economist at the Harvard Business School. He studies economic behavior in a framework based in evolution by natural selection. Susan Lipson is a Lecturer in Anthropology and director of the Reproductive Ecology Laboratory at Harvard University. Her research includes work on the effects of age and energy balance on female reproductive function, and on hormonal correlates of conception and cancer risk. Peter Ellison is John Cowles Professor of Anthropology and Dean of the Graduate School of Arts and Sciences at Harvard University. He studies hormones, behavior, and the reproductive ecology of humans and nonhuman primates.