Analysis of penicillin-binding sites with a micro method — The binding site of PBP 5 from Escherichia coli

Abstract A micro method for the isolation and characterization of the penicillin-binding sites in penicillin-binding proteins (PBPs) was developed. Only 10 nmol of a pure PBP are required for the whole procedure which is based on high-pressure liquid chromatography (HPLC). We showed that serine 44 in PBP 5 from Escherichia coli binds penicillin covalently.     

A spectrophotometric method for the determination of the kinetic parameters of NH+4 uptake by yeast cells

Abstract The kinetic parameters of NH⁺₄-uptake in yeast cells were determined by a method that is based on the following changes in the external NH⁺₄ concentration in cell suspensions by using NADH-dependent glutamate formation from NH⁺₄ and 2-oxoglutarate. The kinetics of the observed NADH oxidation were analyzed by computer and enabled an estimation of V _max and K _m of the NH⁺₄-uptake system of the cells.     

Cytological observations on the ventromedial hypothalamic nucleus

Two sorts of neurons are recognized in Golgi impregnations of the rat ventromedial hypothalamic nucleus (HVM). The two cell types, category I and II neurons, are differentiated on the basis of their somatic, dendritic, and axonal characteristics. Category I neurons form most of the neuronal population and are located throughout HVM. The small number of category II neurons that have been studied occur in lateral HVM. Two varieties of neuronal profile, "common" and "uncommon cells", are seen in thin sections of HVM. The "uncommon cells", in comparison with the "common ones", appear to have a larger soma, a more electron-dense cytoplasmic matrix, an abundance of Nissl bodies, and a population of dense-cored vesicles (100--130 nm in diameter). Some of the somata and proximal dendrites of "common", but not "uncommon" cells, are wrapped in multiple layers of astrocytic processes. Although the correlation is tentative, it is argued that category I neurons correspond to "common cells" and category II, to "uncommon cells". One possible implication of this correspondence is discussed regarding neuronal alteration in response to change in the endocrinological environment of the brain.     

A probability model for the number of births in an equilibrium birth process

A probability model for the number of complete conceptions (that is, live births) taking into account foetal wastages, occurring in a couple during a specified period of time (T₀, T₀+T) is developed assuming that the data was collected starting a long time after marriage. A method of estimating some of the underlying parameters is given. The model is applied to data obtained in a Varanasi Survey in 1969–70.     

Role of three basic light reactions in photomovement of desmids

Photoaccumulations in light trap experiments have been studied in the desmids, Cosmarium, Micrasterias and Euastrum. Dependence of accumulation density on exposure time follows saturation curves, while dose response curves show optima. Time-lapse microcinematography and population methods have revealed that all three basic light-induced motor responses known in microorganisms participate in producing photoaccumulations in desmids. During the initial phase the cells are phototactically attracted towards the trap by scattered light. In low light intensity traps photokinetic reactions may play only a minor role, since photokinesis could be evoked only by light intensities100 lx in Cosmarium cucumis. True photophobic reactions have been demonstrated for the first time in desmids. There are two types of phobic responses in desmids: either the cell reverses its movement or it swings sidewise into the new direction. Behaviour of partially shadowed cells suggests that perception of light direction is brough about by simultaneous intensity measurement at two or more sites within the cell.     

Sister chromatid exchange studies for monitoring DNA damage and repair capacity after cytostatics in vitro and in lymphocytes of leukaemic patients under cytostatic therapy.

The effect of various cytostatic drugs was studied on the frequency of sister chromatid exchanges (SCEs) in vitro and in PHA-stimulated lymphocytes of leukaemic patients under cytostatic therapy. The lymphocyte system is a sensitive one for the detection of DNA damage after administration of cytostatic drugs in vitro. Mitomycin C, busulphan, vincristine, chlorambucil, cytosine arabinoside, cyclophosphamide and lycurim were tested. All except cyclophosphamide induced high frequencies of SCEs in the first mitosis after their administration. The experiments with PHA-stimulated lymphocytes in vivo from patients treated with cytostatics showed that cytosine arabinoside, in combination with thioguanine, did not induce higher frequencies of SCEs, whereas in patients who were treated with cyclophosphamide alone or in combination with other cytostatic drugs, there was a higher incidence of SCEs during treatment. About 10 days after the termination of the treatment the elevated freuqencies of SCEs returned to the initial level. After administration of some mutagens, especially alkylating agents in vivo, the lymphocyte system can be used to assess induced DNA repair by continuously monitoring for SCEs.     

MIXED MODEL APPROACHES FOR ESTIMATING GENETIC VARIANCES AND COVARIANCES

The limitations of methods for analysis of variance(ANOVA)in estimating genetic variances are discussed. Among the three methods(maximum likelihood ML, restricted maximum likelihood REML, and minimum norm quadratic unbiased estimation MINQUE)for mixed linear models, MINQUE method is presented with formulae for estimating variance components and covariances components and for predicting genetic effects. Several genetic models, which cannot be appropriately analyzed by ANOVA methods, are introduced in forms of mixed linear models. Genetic models with independent random effects can be analyzed by MINQUE(1)method whieh is a MINQUE method with all prior values setting 1. MINQUE(1)method can give unbiased estimation for variance components and covariance components, and linear unbiased prediction (LUP) for genetic effects. There are more complicate genetic models for plant seeds which involve correlated random effects. MINQUE(0/1)method, which is a MINQUE method with all prior covariances setting 0 and all prior variances setting 1, is suitable for estimating variance and covariance components in these models. Mixed model approaches have advantage over ANOVA methods for the capacity of analyzing unbalanced data and complicated models. Some problems about estimation and hypothesis test by MINQUE method are discussed.     

畜禽遗传资源冷冻保存中的取样方法探讨

本文基于遗传学和数理统计原理,提出了运用冷冻生殖细胞的方法长期保存畜禽遗传资源时,冷冻生殖细胞的4种取样方法,并推证了其误差公式和最低保存数量的估计公式。最后通过实例对公式的实际应用作了说明和讨论分析。     

Different rates of substitution may produce different phylogenies of the eutherian mammals

Summary In an attempt to resolve some points of branching order in the phylogeny of the eutherian mammals, a phylogenetic analysis of 26 nuclear and 6 mitochondrial genes was undertaken using a maximum likelihood method on a constant rate stochastic model of molecular evolution. Seventeen of the nuclear genes gave a primates/artiodactyls grouping highest support whereas three of the mitochondrial genes found a rodents/artiodactyls grouping to be best supported. The primates/rodents grouping was never the best supported. On the assumption that rodents are indeed an outgroup to primates and artiodactyls and that the latter taxa diverged 70 million years ago, an estimation was made, for each gene, of the time of divergence of the rodent lineage. In most cases such estimates were beyond the limits set by present interpretations of the paleontological record as were many estimates of the divergence time of mouse and rat. These results suggest that, although there is locus variation, the divergent position of the rodent lineage may be an artifact of an elevated rate of nucleotide substitution in this order.