Trypanosoma brucei: analysis of relapsing populations in sensitive and resistant breeds of cattle

The clone DiTat 1.1 of Trypanosoma brucei brucei was injected into four bovids, and clones obtained from successive waves of parasitemia were used to study the expressed variant-specific surface glycoprotein repertoire. Twenty-four clones were obtained which could be classified into 12 different variable antigen types, in addition to the clone injected, using agglutination or immunofluorescence with monospecific antisera. The variable surface glycoproteins of the 25 clones were extracted using the detergent octyl-beta-D-glucopyranoside in the presence of the protease inhibitor, N-cbz-L-phenylalaninechloromethylketone. The molecular weights varied from 52,000 to 69,000 and the pI from 5.0 to 8.8. The virulence of 14 clones representing 13 variable antigen types was ascertained in mice. The mean survival time ranged from 20.5 to 43.0 days. Clones isolated from early peaks of parasitemia in the bovid were the most virulent while clones derived from later peaks were less virulent. It seems that organisms of diminishing virulence appear in bovids, leading to self-cure of the disease. All clones were sensitive to human serum in a blood infectivity inhibition test. Antibody against all virulent clones appeared in 20 cattle (10 Zebus, 10 Baoulés) which had been injected with T. brucei DiTat 1.1. There was no evidence for parasites of high or low virulence being preferentially expressed in resistant or sensitive hosts.     

Identification of the peptide bond cleaved during activation of human Clr

CNBr cleavage of unreduced proenzyme Clr yielded fragment CP2b, isolated by gel filtration and highpressure gel permeation chromatography. This fragment (˜ M_τ 55000) comprised at least 4 disulphidelinked peptides, which were separated by gel filtration after reduction and alkylation. Peptide CP2bRA4, overlapping the A- and B-chain regions in proenzyme Clr was digested by V8 staphylococcal protease, and the digest separated by reversed-phase HPLC. N-terminal sequence analysis of peptide CP2bRA4SP9 established that Clr activation involves the cleavage of a single Arg-Ile bond, located in the sequence: Gln-Arg-Gln-Arg-Ile-Ile-Gly-Gly     

Partial Purification and Properties of Human Brain Aldehyde Dehydrogenases

Acetaldehyde and biogenic aldehydes were used as substrates to investigate the subcellular distribution of aldehyde dehydrogenase activity in autopsied human brain. With 10 microM acetaldehyde as substrate, over 50% of the total activity was found in the mitochondrial fraction and 38% was associated with the cytosol. However, with 4 microM 3,4-dihydroxyphenylacetaldehyde and 10 microM indoleacetaldehyde as substrates, 40-50% of the total activity was found in the soluble fraction, the mitochondrial fraction accounting for only 15-30% of the total activity. These data suggested the presence of distinct aldehyde dehydrogenase isozymes in the different compartments. The mitochondrial and cytosolic fractions were, therefore, subjected to salt fractionation and ion-exchange chromatography to purify further the isozymes present in both fractions. The kinetic data on the partially purified isozymes revealed the presence of a low Km isozyme in both the mitochondria and the cytosol, with Km values for acetaldehyde of 1.7 microM and 10.2 microM, respectively. However, the cytosolic isozyme exhibited lower Km values for the biogenic aldehydes. Both isozymes were activated by Mg2+ and Ca2+ in phosphate buffers (pH 7.4). Also, high Km isozymes were found in the mitochondria and in the microsomes.     

Immunoassay of the Neuronal and Neuroendocrine Marker PGP 9.5 in Human Tissues

An inhibitory, coated-well immunoassay for the neurone-specific protein PGP 9.5 has been devised and used to measure the concentrations of the protein in human tissues. Concentrations of PGP 9.5 between 40 ng/ml and 10 micrograms/ml could be measured using this assay. In brain PGP 9.5 was present at 100.58 +/- 16.18 micrograms/mg protein. Of the other organs examined only kidney and testis showed significant concentrations of PGP 9.5 (3.97 +/- 0.87 microgram/mg protein and 3.25 +/- 0.36 microgram/mg protein, respectively). All other organs contained less than 2% of the brain level. The tissue levels determined by coated-well immunoassay confirmed the tissue specificity of PGP 9.5 originally determined by high-resolution two-dimensional gel electrophoresis.     

A continuum model to study the internal fluctuations in globular proteins

The salient features of the differential equation model to study protein dynamics are presented with results for 19 proteins.     

Diffusion of inorganic carbon across an unstirred layer: a simplified quantitative approach

Abstract The quantitative approach used here is based on a model comprising a well-stirred medium, an unstirred layer, and a CO₂ absorbing leaf. The unstirred layer is divided up by planes into a number of sub-layers. Within each plane the concentration of each solute is everywhere the same as is the electric potential. These variables constitute the basic data. Thus the planes were characterized by their pH value. An equation is derived which enables the calculation of the basic data of a plane from the known data of another plane. In this way it is possible to calculate the basic data for all planes. From these data the rate of assimilation, the thickness of the unstirred layer and its sub-layers, the fluxes across the sub-layers and the conversions among the carbon components can be estimated. The CO₂ flux decreases, and the HCO^?₃ flux increases towards the leaf. There are negative fluxes of OH^& and CO^2–₃. H⁺ fluxes are of minor importance and can be ignored if the pH of the medium is higher than 8.0, provided no non-inorganic C buffers with appropriate pK_a are present. The significance of the carbon diffusion facilitating effect of an inorganic carbon system is expressed in various ways. The values obtained represent maxima, as the assumption is made that the equilibrium reactions are very fast. It is argued that even better effects are possible if the back-diffusion of CO^2–₃ could be prevented by lowering the pH of the unstirred layer.     

丁酸对体外培养的人鼻咽癌上皮细胞的影响

无论是自发的、病毒引起的或致癌物诱发的恶性转化的哺乳类细胞的体外培养,其形态多发生改变,总是变得近似圆形,边缘突起短而少,细胞致密和折光性强,同时失去生长接触抑制,降低细胞与细胞之间和细胞与生长底物之间的粘着性等特性。近年报道了关于短链脂肪酸如丁酸(或丁酸钠)对细胞能产生明显的影响,能抑制培养细胞的分裂,可诱发一些上皮性细胞产生形态的改变,可使转化的细胞     

用PFU法研究微型生物群集过程中数据的处理

根据MacArthur-Wilson的岛屿区系平衡模型S_t=S_(eq)(1-e~(GT)),可以从野外生态效应试验和室内毒性试验中,提出3个功能参数(S_(eq)、G、t_(90％))进行比较。本文提出两种计算方法:复合梯形法和最小二乘法,后者已在计算机上实现了BASIC计算程序。从数学理论上论证,最小二乘法误差较小,但如果实验布局合理,两种计算方法能得到十分一致的结果。实验模型是否符合理论模型,可以用统计学上的拟合差异度检验法来检验。     

Global asymptotic stability of the size distribution in probabilistic models of the cell cycle

Probabilistic models of the cell cycle maintain that cell generation time is a random variable given by some distribution function, and that the probability of cell division per unit time is a function only of cell age (and not, for instance, of cell size). Given the probability density, f(t), for time spent in the random compartment of the cell cycle, we derive a recursion relation for _n(x), the probability density for cell size at birth in a sample of cells in generation n. For the case of exponential growth of cells, the recursion relation has no steady-state solution. For the case of linear cell growth, we show that there exists a unique, globally asymptotically stable, steady-state birth size distribution, _*(x). For the special case of the transition probability model, we display _*(x) explicitly.This work was supported by the National Science Foundation under grants MCS8301104 (to J.J.T.) and MCS8300559 (to K.B.H.), and by the National Institutes of Health under grant GM27629 (to J.J.T.).     

A prediction model for parasitic gastro-enteritis in lambs

Paton G., Thomas R. J. and Waller P. J. 1984. A prediction model for parasitic gastroenteritis in lambs. International Journal for Parasitology14: 439–445. The parasite Ostertagia circumcincta is a major cause of parasitic gastro-enteritis in lambs in temperate countries. A prediction model is described, based on a mathematical representation of the external and internal stages of the life-cycle.The model is used to predict the numbers of infective larvae on a permanent experimental paddock grazed by ewes and lambs in 1973 and 1974. The “moisture status” of the surface layer of the pasture was found to be of fundamental importance for the successful prediction of the development and survival of the pre-infective larval stages. For the years studied the contribution to the summer wave of infection by lamb derived larvae was particularly significant.