The control of incompatibility in distylous Pulmonaria affinis Jordan (Boraginaceae)

In P. affinis, pin pollen is shorter on average than thrum pollen. Pins have more coronal hooks on stigmatic papillae than thrums, but gaps between papillae are relatively smaller for thrums. Pin stigmas receive more pollen than thrum stigmas. Thrum stigmas receive more (dissortive) pin pollen, but pin stigmas are assortively pollinated. Pollen only germinates when trapped below papilla coronas. On thrum stigmas, most trapped pollen is pin. Pollen germination is better on thrum stigmas than pin stigmas, and thrum stigmas show a close relationship between numbers of legitimate pollen grains, numbers of germinating grains, and numbers of pollen tubes in the style. There is no inhibition of illegitimate pollen germination. Illegitimate pollen tubes are inhibited in the style. Incompatibility operates by a combination of dissortive pollination, dissortive pollen trapping, and stylar pollen tube inhibition. All heteromorphic features differing between pins and thrums are implicated in the inhibition of within-morph fertilization in thrums.     

Effects of three herbicides on soil microbial biomass and activity

Three post-emergence herbicides (2,4-D, picloram and glyphosate) were applied to samples of an Alberta agricultural soil at concentrations of 0, 2, 20, and 200 μg g⁻¹. The effects of these chemicals on certain microbial variables was monitored over 27 days. All herbicides caused enhancement of basal respiration but only for 9 days following application, and only for concentrations of 200 μg g⁻¹. Substrate-induced respiration was temporarily depressed by 200 μg g⁻¹ picloram and 2,4-D, and briefly enhanced by 200 μg g⁻¹ glyphosate. It is concluded that because changes in microbial variables only occurred at herbicide concentrations of much higher than that which occurs following field application, the side-effects of these chemicals is probably of little ecological significance.     

Hemolysis of rabbit erythrocytes in the presence of copper ions

The hemolysis of red blood cells (RBC) induced by Cu(II) is modified by ceruloplasmin (Cp) and albumin. The time course of hemolysis for rabbit RBC by Cu(II) consisted of two parts, an induction period followed by a catastrophic lysis period. The induction period decreased and the lysis rate increased with increasing Cu(II) concentration. Cp or albumin, modified Cu(II) induced hemolysis, by increasing the duration of the induction period and decreasing the overall rate of hemolysis of RBC. The catastrophic lysis period coincided with a sharp increase in the formation of metHb within the cell and in a rapid uptake of Cu(II). The presence of Cp led to an increase in the induction period prior to the rapid increase in metHb formation and in Cu(II) uptake. Porcine Cp was prepared with either two or three nonprosthetic copper binding sites (sites where Cu(II) is easily removed by passing over Chelex-100). Cp with three nonprosthetic binding sites gave more protection than Cp with two. Likewise, albumin can be prepared with three and five nonprosthetic copper binding sites. The albumin with five sites gave more protection than the albumin with three sites.     

多羟基苯衍生物对逆转录酶抑制动力学的研究

 一些多羟基苯衍生物对逆转录酶呈现竞争性抑制作用,它们对M-MLV逆转录酶的抑制作用比AMV逆转录酶要强。     

Influence of single amino acids on the development of hamster one-cell embryos in vitro

One-cell hamster embryos placed in culture have always shown a complete block to development at the two-cell stage. In a preliminary study using a chemically defined culture medium containing 20 amino acids (HECM-1), many one-cell embryos were able to escape the "two-cell block" and develop to the four-cell stage. Use of a simpler formulation containing only the amino acids hypotaurine and glutamine revealed marked inhibitory and stimulatory effects of adding the other amino acids. In the first experiment, 19 amino acids were separately examined for effects on one-cell embryo development. Six amino acids (phenylalanine, valine, isoleucine, tyrosine, tryptophan, and arginine) inhibited embryo development (reduced mean cell number; MCN), and three others (glycine, cystine, and lysine) stimulated development (increased MCN), compared with basic medium containing only glutamine and hypotaurine (low control). When the responses with the six inhibitory amino acids were totalled, only 3 of 185 (2%) one-cell embryos reached the six-or seven-cell stage compared to a total of 15 of 76 (20%) embryos that developed to these stages using the three stimulatory amino acids. When tested together in a second experiment, the six inhibitory amino acids significantly reduced the MCN, from 4.28 +/- 0.44 (low control) to 3.71 +/- 0.55. In this group, 17 of 117 (15%) of one-cell embryos reached more than four-cell and only 4 of 117 (3%) reached six- or 7-cell stages, compared with 39 of 117 (33%) and 12 of 117 (10%), respectively, for the basal medium group.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of sulfate reduction on the thermophilic (55°C) methane fermentation process

Summary The continuously operated suspended growth anaerobic contact system was utilized to estimate the effect of sulfate reduction on the thermophilic (55°C) methane fermentation process. Results indicated that reduction in methanogenesis in the presence of sulfate was due to two separate, but related, processes;i.e. competitive and sulfide inhibition. Although prevention of competitive inhibition would be difficult under normal fermenter operation, sulfide inhibition could be minimized by environmental selection of sulfide tolerant microbial populations through biomass recycle and pH control. Stable fermenter operation was achieved at soluble sulfide concentrations as high as 330 mg/l soluble sulfide. Using batch fermenters, a maximum thermophilic sulfate reduction rate of 3.7 mg SO₄ ^2––S/g volatile solids (VS)-day was estimated. The importance of reporting sulfate reduction rates on a biomass basis is demonstrated by a simple population adjustment kinetic model.This research study was conducted at the Department of Agricultural Engineering, Cornell University, Riley Robb Hall, Ithaca, NY 14853, U.S.A.     

Metrifonate and dichlorvos: Effects of a single oral administration on cholinesterase activity in rat brain and blood

Cholinesterase activities in rat forebrain, erythrocytes, and plasma were assessed after a single oral administration of metrifonate or dichlorvos. In 3-month-old rats, the dichlorvos (10 mg/kg p.o.)-induced inhibition of cholinesterase reached its peak in brain after 15–45 min and after 10–30 min in erythrocytes and plasma. Cholinesterase activity recovered rapidly after the peak of inhibition, but did not reach control values in brain and erythrocytes within 24 h after drug administration. The recovery of plasma cholinesterase activity, in contrast, was already complete 12 h after dichlorvos treatment. Metrifonate (100 mg/kg p.o.) had qualitatively similar inhibition kinetics as dichlorvos, albeit with a slightly delayed onset. Peak values were attained 45–60 min (brain) and 20–45 min (blood), after drug administration. Apparently complete recovery of cholinesterase activity was noted in both tissues 24 h after treatment. The dose-dependence of drug-induced inhibition of cholinesterase in rat blood and brain was determined at the time of maximal inhibition, i.e., 30 min after dichlorvos treatment and 45 min after metrifonate treatment. The oral ED₅₀ values obtained for dichlorvos were 8 mg/kg for brain and 6 mg/kg for both erythrocyte and plasma cholinesterase. The corresponding oral ED₅₀ values for metrifonate were 10 to 15 times higher, i.e., 90 mg/kg in brain and 80 mg/kg in erythrocytes and plasma. In rats deprived of food for 18 h before drug treatment, the corresponding ED₅₀ values for metrifonate were 60 and 45 mg/kg, respectively, indicating an about two-fold higher sensitivity of fasted rats to metrifonate-induced cholinesterase inhibition compared to non-fasted rats. Compared to 3-month-old rats, 19-month-old rats showed a higher sensitivity towards metrifonate and dichlorvos. At the time of maximal inhibition, there was a strong correlation between the degree of cholinesterase inhibition in brain and blood. These results demonstrate that single oral administration of metrifonate and dichlorvos induces an inhibition of blood and brain cholinesterase in the conscious rat in a dose-dependent and apparently fully reversible manner. While the efficiency of a given dose of inhibitor may vary with the satiety status or age of the animal, the extent of brain ChE inhibition can be estimated from the level of blood ChE activity.     

Treatment of Gaucher disease with an enzyme inhibitor

The hypothesis is offered predicting that Caucher patients could be treated with a drug that slows the synthesis of glucosylceramide, the lipid that accumulates in this disorder. The present therapeutic approach involves augmenting the defective enzyme, glucosylceramide -glucosidase, with exogenous -glucosidase isolated from human tissue. This spectacularly expensive mode of treatment should be replaceable with a suitable enzyme inhibitor that simply slows formation of the lipid and matches the rate of synthesis with the rate of the defective, slowly working -glucosidase. Several drugs that possess this ability are available, the best known of which is 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), a designer inhibitor that resembles the synthase's substrate and product. PDMP has been found to be effective in mice, rats, fish, and a wide variety of cultured cells. Its use, at suitable dosages, seems to be harmless, although long-term tests have not been made. The lack of suitable animal models of Gaucher disease has made it difficult to test the hypothesis adequately, but PDMP does rapidly lower the levels of glucosylceramide in normal animal tissues and the animals evidently do well with the lowered levels of glucosylceramide and its more complex glycolipid metabolites.Abbreviations PDMP 1-phenyl-2-decanoylamino-3-morpholino-1-propanol - GlcCer glucosylceramide - i.p. intraperitoneal     

Studies on activation and inhibition of cathepsin B from buffalo liver

Cathepsin B (EC 3.4.22.1) was purified from buffalo liver. The enzyme activity against-benzoyl-dl-arginine-naphthylamme (BANA) was substantially reduced by heat (above 37C) and by nondenaturing concentrations of urea (3 M) and guanidine hydrochloride (1 M). Cathepsin B was significantly activated by 1.5 mM EDTA alone. The activation of the enzyme was further enhanced in the presence of thiol compounds, e.g., cysteine thioglycolic acid, 2,3-dimercapto-1-propenol, and dithioerythritol (DTE). The minimum concentration of the thiol compound required for optimal activation of cathepsin B was found to be lowest (0.2 mM) for DTE. The BANA hydrolyzing activity of cathepsin B was substantially reduced by Cu²⁺ (20–200M) and Ca²⁺ (30–250 mM) as well as by thiol blocking reagents, e.g., iodoacetate, 5,5-dithiobis(2-nitro-benzoic acid) (DTNB), andp-hydroxymercuribenzoate (pHMB). The enzyme activity was completely abolished when the molar ratio of the reagent: cathepsin B was close to 1. The number of free sulfhydryl groups in cathepsin B was determined to be 2 by titration against DTNB and pHMB. Modification of one free thiol group of cathepsin B resulted in complete loss of BANA hydrolyzing activity.