INHIBITION OF NITRIFICATION BY CLIMAX ECOSYSTEMS

Three plots representing two stages of old-field succession and the climax were selected in each of three vegetation types in Oklahoma: oak-pine forest, post oak-blackjack oak forest, and tall grass prairie. Soil samples from the 0–15 and 45–60 cm levels were analyzed every other month for 1 yr for exchangeable ammonium nitrogen and for nitrate. On alternate months numbers of Nitrosomonas and Nitrobacter were determined in the 0–15 cm level. The amount of ammonium nitrogen was lowest in the first successional stage, intermediate in the second successional stage, and highest in the climax stand. This trend was remarkably consistent throughout all sampling periods, all vegetation types, and both sampling levels in the soil. The amount of nitrate was highest in the first successional stage, intermediate in the second successional stage, and lowest in the climax stand in both sampling levels, all vegetation types, and virtually all sampling periods. The numbers of nitrifiers were high in the first successional stage, generally, and decreased to a very low level in the climax. In fact, there was often no Nitrobacter in the climax stands. These results indicate that the nitrifiers are inhibited in the climax so that ammonium nitrogen is not oxidized to nitrate as readily in the climax as in the successional stages. Evidence from other geographic areas and vegetation types strongly supports this conclusion. This would certainly appear to be a logical trend in the evolution of ecosystems because of the increased conservation of nitrogen and energy. The ammonium ion is positively charged and is adsorbed on the negatively charged colloidal micelles, thus preventing leaching below the depth of rooting. On the other hand, nitrate ions are negatively charged, are repelled by the colloidal micelles in the soil, and thus readily leach below the depth of rooting or are washed away in surface drainage. There is growing evidence also that many plant species can use ammonium nitrogen as effectively or more so than nitrate nitrogen. If ammonium nitrogen is used directly, this eliminates four chemical steps because nitrogen which is oxidized to nitrite and then to nitrate must be reduced back to nitrite and then to ammonium nitrogen before it can react with keto-acids in the formation of amino acids. The two reduction reactions require considerable expenditure of energy.     

蛋白酶抑制剂对小鼠胚泡着床的作用

本文采用子宫内注射和胚胎与子宫上皮细胞在体外共培养的方法,研究几种蛋白酶抑制对小鼠胚胎着床的影响。实验结果显示,蛋白酶抑制剂ＳＴＩ,ＥＡＣＡ和ＮＰＧＢ均能显著抑制胚泡在子宫内着床;ＳＴＩ和ＥＡＣＡ能有效地抑制胚泡在子宫上皮细胞单层上的扩展,而ＮＰＧＢ对胚泡在子宫上皮细胞单层上的粘附和扩展均有显著的抑制作用。     

THE INHIBITION OF CYPRIDINA LUMINESCENCE BY LIGHT

The luminescence of Cypridina luciferin-luciferase solution is inhibited by illumination from a carbon arc of 15,000 foot candles in between 1 and 2 seconds. The blue to violet rays are the effective ones, the limits lying somewhere around 4,600 Å. u. to 3,800 Å. u. The luciferin, not the luciferase, is the substance affected by the light. The effect is partially reversible in the dark. The chemiluminescences obtained by oxidizing phosphorus, lophin, and chlorphenylmagnesium bromide are not inhibited by light under the above conditions.     

INHIBITION BY BACTERIA OF PSEUDOPLASMODIUM FORMATION OF DICTYOSTELIUM DISCOIDEUM

A mutant of Dictyostelium discoideum was isolated, the development of which was normal at 18.5°C but stopped at the aggregate stage when cultured with bacterial associate at 26°C. Probably the bacteria release a factor inhibitory to pseudoplasmodium formation, the inactivation of the inhibitor being temperature-sensitive in this mutant. This bacterial factor is different from the one reported by W eber and R aper (16), judging from the synergism shown by these two types of mutants.
The temperature-shift experiment gave the result that the inhibited developmental step was at about the time of initiation of tip formation. However, once a tip was formed under the permissive conditions, the re-formation of a new tip after removal of the original was not inhibited under the nonpermissive conditions. These results indicate that the bacterial inhibitor acts just before tip formation.     

类胡萝卜素对亚油酸甲酯氧化的抑制作用

研究溶液中类胡萝卜素对2 ,2’ -偶氮二 (2 ,4短杠二甲基戊腈 ) (AMVN)引发的亚油酸甲酯氧化的抑制作用及色素的消耗变化。表明 β-胡萝卜素 ,叶黄素及胭脂树橙都按依赖于剂量的方式抑制亚油酸甲酯氢过氧化物的形成。41.7×10 -6mol/L的叶黄素及玉米黄质的抑制活性相近 ,高于β-胡萝卜素与胭脂树橙的活性 ,后两者活性近似。在83.3×10 -6mol/L浓度下鸡油菌黄质活性高于叶黄素 ,后者又高于 β-胡萝卜素与胭脂树橙 ,最后两者仍近似。结果表明下列五种类胡萝卜素对亚油酸甲酯氧化的抑制能力为 :鸡油菌黄质>玉米黄质≈叶黄素> β-胡萝卜素≈胭脂树橙。类胡萝卜素在抑制脂质氧化过程中 ,本身逐渐损失消耗 ,4h后在试验所用浓度下最高剩余量不超过20 %。其中鸡油菌黄质与胭脂树橙的消耗速度慢于 β-胡萝卜素与玉米黄质。     

INHIBITION OF FERN SPORE GERMINATION BY LIPOPHILIC SOLVENTS

Several alcohols and other solvents inhibit germination of spores of the fern, Onoclea sensibilis L. The inhibition is reversible when spores are transferred to solvent-free media. The effectiveness of different solvents, measured by the concentration needed to inhibit germination by 50%, increases with their lipid solubility. The activity of straight-chain alcohols from methanol through n-heptanol is highly correlated with lipid solubility, whereas the correlation is weaker for several other solvents. The results indicate that some lipophilic site in the spore is important in germination.     

有机磷杀虫剂使家蝇中毒后对酯酶的抑制作用

本文研究了乐果、敌百虫和TOCP等三种药剂对家蝇胆碱酯酶与脂族酯酶的体内抑制与中毒症状之间的关系。试验以家蝇为材料,用上述药剂的LD₅₀剂量处理后观察其在不同时间内的中毒症状,并用Warburg测压法分别在不同时间内测定家蝇头部和胸腹部胆碱酯酶和脂族酯酶的抑制情况 所得结果表明:无论头部和胸腹部胆碱酯酶的抑制程度都与中毒症状密切相关。当家蝇中毒倒伏时胆碱酯酶的活性最低。脂族酯酶的抑制作用与中毒症状虽有一定的关系,但是单独抑制脂族酯酶不表现出任何症状。因此,可以认为有机磷杀虫剂的主要中毒作用是抑制胆碱酯酶,虽然也可能是两种酶同时受抑制的作用。     

双歧杆菌体外对STM拮抗作用的实验研究

研究休外双歧杆菌对鼠伤寒沙门菌的拮抗作用,方法将两歧双歧杆菌ＳＴＭ混合培养。观察ＳＴＭ生长情况。结果ＳＴＭ和Ｂ．ｂｉｆｉｄｕｍ混合培养与ＳＴＭ单独培养对照相比较,菌量明显降低。结论Ｂ．ｂｉｆｉｄｕｍ在体外对ＳＴＭ有拮抗作用。     

INHIBITION OF ACETYLCHOLINESTERASE IN VITRO BY PENTYLENETETRAZOL1

Abstract—The effect of pentylenetetrazol (PTZ) on acetylcholinesterase (E.C.3.1.1.7) was studied in vitro. The kinetics of the reaction were studied on AChE in crude homogenates of rat brain and in purified preparations from Electrophorus electricus. The K_m for rat brain AChE was 1·22 × 10^-4m, with a V_max of 1·37 μmol/g/min whereas the K₄ for competitive inhibition of the enzyme by PTZ was 4·7 × 10^-3m. The commercially purified enzyme exhibited a K_m of 1·73 × 10^-4m and a K_i of 1·00 × 10^-3m.