Reductive biotransformations of organic compounds by cells or enzymes of yeast.

Saccharomyces cerevisiae catalyses the asymmetric reductive biotransformation of a variety of compounds containing a carbonyl group or carbon-carbon double bond. Oxidoreductases participating in these reactions which have commercial potential in biotransformation processes are likely to have relatively broad substrate specificity. Important carbonyl reductases falling into this category include YADH- and yeast NADP-dependent beta-ketoester reductases. The enoyl reductase component of the FAS complex may have a role in asymmetric yeast reduction of carbon-carbon double bonds of unnatural substrates. Other nicotinamide-requiring oxidoreductases of yeast are also surveyed to rationalize observed biotransformations of whole yeast cells in terms of specific enzymes. Genetic and protein engineering may enable enzymes to be tailored to accept new substrates. A greater understanding of the enzymes and reactions involved will facilitate further optimization and exploitation of these catalytic systems in industrial processes.     

3H]L-657,743 (MK-912): a new, high affinity, selective radioligand for brain alpha 2-adrenoceptors

L-657,743 (MK-912), a highly potent and selective alpha 2-adrenoceptor antagonist was tritiated to a high specific activity and its binding characteristics to brain tissue were determined. The specific binding of [3H]L-657,743 to rat cerebrocortex was saturable, reversible, and dependent on tissue concentration. In saturation studies, [3H]L-657,743 binding was resolved into two high affinity components exhibiting Kd values of 86 pM and 830 pM with densities of 82 fmol/mg protein and 660 fmol/mg protein, respectively. Based on the binding potencies of a variety of compounds with differing receptor selectivities, the sites labeled by [3H]L-657,743 were characteristic of alpha 2-adrenoceptors. In contrast to alpha 2-antagonists, alpha 2-agonists displayed shallow competition curves. In the presence of 100 microM GTP, Gpp(NH)p or 150 mM NaCl, the competition curve for epinephrine was shifted to the right, whereas that for yohimbine was unaffected. In studies utilizing human cerebrocortical tissue, [3H]L-657,743 also bound with high affinity to sites characteristic of alpha 2-adrenoceptors.     

Chromogenic redox assay for beta-lactamases yielding water-insoluble products. II. Heterogeneous sandwich assay for hCG.

A very sensitive and rapid heterogeneous sandwich enzyme immunoassay for human chorionic gonadotropin (hCG) is described. The assay is based on the application of the novel chromogenic redox substrate system for beta-lactamase which is used as label. The chromogen system consists of a thioacetylcephalosporin beta-lactamase substrate, which upon turnover by the enzyme label releases the thiolate with the concomitant reduction of the tetrazolium salt to a colored formazan. The concentration of the formazan is directly related to the amount of the hormone in the sample and is read spectrophotometrically. The enzyme-antibody conjugates, produced through use of heterobifunctional maleimide crosslinker, maintain 90% of the enzyme activity after 30 days at 25 degrees C. Concentrations of the hormone as low as 5 mIU/ml, equivalent to 25 fmol/ml, are detectable in 3 h.     

Control of the Amiloride-Sensitive Na+ Current in Salivary Duct Cells by Extracellular Sodium

We have previously reported that intralobular salivary duct cells contain an amiloride-sensitive Na⁺ conductance (probably located in the apical membranes). Since the amiloride-sensitive Na⁺ conductances in other tight epithelia have been reported to be controlled by extracellular (luminal) Na⁺, we decided to use whole-cell patch clamp techniques to investigate whether the Na⁺ conductance in salivary duct cells is also regulated by extracellular Na⁺. Using Na⁺-free pipette solutions, we observed that the whole-cell Na⁺ conductance increased when the extracellular Na⁺ was increased, whereas the whole-cell Na⁺ permeability, as defined in the Goldman equation, decreased. The dependency of the whole-cell Na⁺ conductance on extracellular Na⁺ could be described by the Michaelis-Menten equation with a K _m of 47.3 mmol/1 and a maximum conductance (G _max) of 2.18 nS. To investigate whether this saturation of the Na⁺ conductance with increasing extracellular Na⁺ was due to a reduction in channel activity or to saturation of the single-channel current, we used fluctuation analysis of the noise generated during the onset of blockade of the Na⁺ current with 200 μmol/l 6-chloro-3,5-diaminopyrazine-2-carboxamide. Using this technique, we estimated the single channel conductance to be 4 pS when the channel was bathed symmetrically in 150 mmol/l Na⁺ solutions. We found that Na⁺ channel activity, defined as the open probability multiplied by the number of available channels, did not alter with increasing extracellular Na⁺. On the other hand, the single-channel current saturated with increasing extracellular Na⁺ and, consequently, whole-cell Na⁺ permeability declined. In other words, the decline in Na⁺ permeability in salivary duct cells with increasing extracellular Na⁺ concentration is due simply to saturation of the single-channel Na⁺ conductance rather than to inactivation of channel activity. Received: 27 July 1995/Revised: 7 December 1995     

Floristic diversity and co-occurrences in a subtropical broad-leaved forest and two contrasting regrowth stands in central-west Yunnan Province,China

Many of the natural forested ecosystems that still remain in mainland China are being cleared with potentially detrimental effects on woody plant species diversity on both local and regional scales. The most extensive stand of subtropical broad-leaved forest remaining in China is located in Yunnan Province. In an effort to document the influence of human-induced disturbance on Yunnan's woody flora, floristic inventories were conducted in a stand of primary forest and in regrowth stands located in its interior and along its outer margin in the Xujiaba Nature Sanctuary in the Ailao Mountain Range. Of particular interest was the location of the disturbance relative to the primary forest source area. A total of 134 woody plant species representing 74 genera and 43 families were recorded. The floristics of the two regrowth stands were significantly different from each other, with < 10% of their respective floras comprised of co-occurring species. The interior regrowth stand had a higher number of co-occurring species with the primary forest; however, > 40% were still non-co-occurring.The principal families represented in the primary forest and the interior regrowth stand were Aquifoliaceae, Berberidaceae, Fagaceae, Lauraceae, Rosaceae, Smilacaceae, Symplocaceae, Theaceae, and Vacciniaceae. The three dominant species with relative importance values ranging from > 5% to 18% in both the primary forest and the interior regrowth stand were Castanopsis wattii, Lithocarpus jingdongensis, and Symplocos sumuntia. The edge regrowth stands had the lowest species diversity and were dominated by the native pine Pinus yunnanensis, with a relative importance of 24%. The principal families represented in the edge regrowth stand were Betulaceae, Ericaceae, Fagaceae, Myricaceae, Pinaceae, and Theaceae. Only the Fagaceae and Theaceae were well-represented in all three stands. The results of the study document the low species diversity in post-cutting regrowth on the margins of the primary forest as compared with post-cutting regrowth in the forest interior.     

RAPD typing of clinical isolates of Staphylococcus haemolyticus

The randomly amplified polymorphic DNA (RAPD) assay was used to generate DNA fingerprints from clinical isolates of Staphylococcus haemolyticus isolated from patients treated with continuous ambulatory peritoneal dialysis and previously subjected to a combination of typing methods. The RAPD profiles generated with one of six randomly designed 10-mer primers allowed visual discrimination of strains. Good correlation with the original typing scheme was achieved but RAPD typing allowed discrimination of strains previously indistinguishable.     

Comparison of prevalence of schizophrenia among residents of hostels for homeless people in 1966 and 1992.

OBJECTIVE--To determine whether the prevalence of schizophrenia among the homeless population of Edinburgh resident in hostels has changed between 1966 and 1992. DESIGN--Comparison of two cross sectional surveys. SETTINGS--Hostels for homeless people in Edinburgh. SUBJECTS--In 1966 a random sample of 98 residents of three common lodging houses. In 1992 a random sample of 198 residents of nine hostels. MAIN OUTCOME MEASURE--Prevalence of schizophrenia. RESULTS--The prevalence of schizophrenia in 1992 was 12/136 (9%) compared with 20/79 (25%) in 1966 (odds ratio 0.29; 95% confidence interval 0.13 to 0.62; P = 0.001). Adjustment for confounding by age, current hostel, and duration of unemployment by means of logistic regression produced an adjusted odds ratio of 0.22 (0.08 to 0.58). CONCLUSIONS--The prevalence of schizophrenia was lower in 1992 even after other changes in the population resident in hostels occurring between 1966 and 1992 were taken into account. The findings are not consistent with an increase in the prevalence of schizophrenia among homeless people despite a 66% reduction in adult psychiatric beds in the region during 1966-92.