Nitrogen budget of a shortgrass prairie ecosystem

Summary A N budget is presented for a shortgrass prairie ecosystem. The grassland was ungrazed by domestic herbivores. The quantities of N in various plant, animal, microorganism, and soil components of the ecosystem are estimated for the date when aboveground living biomass was at its maximum for the growing season of 1973. Annual transfers of N between the various compartments were also estimated.Of the total N, 99.5% was in organic forms. The relatively inert heteropolycondensate fraction of the organic matter in the soils contained 88.8% of the N. Living organisms contained 4.2% and dead but recognizable organisms or part thereof contained 6.5% of the total N. Belowground animals contained more than 10 times as much N as abovegroud animals, but combined, animals contained less than 0.1% of the total in the system. Living plant material contained 2.5% of the total N. Seventy-two percent of the living plant N was below ground. Microorganisms contained 1.4% of the total N.Total N uptake by plants from soil solution was 2.9 g·m^-2·yr^-1. Aerial portions of plants were allocated 1.9 N·m^-2·yr^-1 although apparently 26% of this amount came from internally recycled sources. The heteropolycondensate fraction of the soil contributed 0.7 g N·m^-2·yr^-1 to mineral forms, but these components of the system were assumed to be in steady state; thus an equal amount of mineral N was allocated back to the source. Mineralization of N from plant residues was sufficient to account for all of the N taken up by plants from soil solution. Soil animals immobilized about 0.4 g N·m^-2·yr^-1 while the amount shunted to aboveground animals was trivial.     

Inhibition by ethanol, acetaldehyde and trifluoroethanol of reactions catalysed by yeast and horse liver alcohol dehydrogenases.

1. Produced inhibition by ethanol of the acetaldehyde-NADH reaction, catalysed by the alcohol dehydrogenases from yeast and horse liver, was studied at 25 degrees C and pH 6-9. 2. The results with yeast alcohol dehydrogenase are generally consistent with the preferred-pathway mechanism proposed previously [Dickenson & Dickinson (1975) Biochem. J. 147, 303-311]. The observed hyperbolic inhibition by ethanol of the maximum rate of acetaldehyde reduction confirms the existence of the alternative pathway involving an enzyme-ethanol complex. 3. The maximum rate of acetaldehyde reduction with horse liver alcohol dehydrogenase is also subject to hyperbolic inhibition by ethanol. 4. The measured inhibition constants for ethanol provide some of the information required in the determination of the dissociation constant for ethanol from the active ternary complex. 5. Product inhibition by acetaldehyde of the ethanol-NAD+ reaction with yeast alcohol dehydrogenase was examined briefly. The results are consistent with the proposed mechanism. However, the nature of the inhibition of the maximum rate cannot be determined within the accessible range of experimental conditions. 6. Inhibition of yeast alcohol dehydrogenase by trifluoroethanol was studied at 25 degrees C and pH 6-10. The inhibition was competitive with respect to ethanol in the ethanol-NAD+ reaction. Estimates were made of the dissociation constant for trifluoroethanol from the enzyme-NAD+-trifluoroethanol complex in the range pH6-10.     

Estimation of rate dissociation constants involving ternary complexes in reactions catalysed by yeast alcohol dehydrogenase

Stopped-flow studies of oxidation of butan-1-ol and propan-2-ol by NAD(+) in the presence of Phenol Red and large concentrations of yeast alcohol dehydrogenase give no evidence for the participation of a group of pK(a) approx. 7.6 in alcohol binding. Such a group has been implicated in ethanol binding to horse liver alcohol dehydrogenase [Shore, Gutfreund, Brooks, Santiago & Santiago (1974) Biochemistry13, 4185-4190]. The present result supports previous findings based on steady-state kinetic studies with the yeast enzyme. Stopped-flow studies of the yeast alcohol dehydrogenase-catalysed reduction of acetaldehyde by NADH in the presence of ethanol as product inhibitor indicate that the rate-limiting step is NAD(+) release from the enzyme-NAD(+)-ethanol product complex. This finding permits calculation of K(3), the dissociation constant for ethanol from the enzyme-NAD(+)-ethanol complex, by using the product-inhibition data of Dickenson & Dickinson (1978) (Biochem. J.171, 613-627). The calculations show that K(3) varies very little with pH in the range 5.95-8.9, and this agrees with the findings of the stopped-flow experiments described above. Absorption and fluorescence measurements on mixtures of substrates and coenzymes in the presence of high concentrations of alcohol dehydrogenase have been used to estimate values for the ratio [enzyme-NADH-acetaldehyde]/ [enzyme-NAD(+)-ethanol] at equilibrium. The values obtained were in the range 0.11+/-0.04, and this value together with estimates of K(3) was used to provide estimates of values for rate constants and dissociation constants for steps within the catalytic mechanism.     

5-羟色胺诱发的主动脉区化学感受性升血压反射中某些区域性血管反应的分析

在15只麻醉开胸犬中,用在体器官恒流灌注法研究了骨胳肌、皮肤、肾和心脏的血管在5-HT 诱发的主动脉区化学感受性升血压反射中的反应,同时还观察了5-HT 对这些器官血管的直接效应。左心房注入5-HT(200μg)后,在动脉血压急剧上升的同时,股薄肌、皮肤(后爪)和肾脏的灌流压明显增加,其增值分别为43±8.47±5和56±27mmHg(P<0.01),而冠脉灌流压无明显改变。用阿托品和/或心得安阻断骨胳肌、皮肤和心脏灌流区域的 m 和同β-受体后,上述效应无进一步变动。向灌流环路直接注入5-HT(10—50μg),可引起皮肤和肾脏的血管收缩,而股薄肌和心肌的血管则扩张;后一效应不被心得安阻断。以上结果提示:1.在5-HT 诱发的主动脉区化学感受性升血压反射中,骨胳肌、皮肤和肾脏呈现明显的交感性缩血管反应,而并不伴有交感性扩血管活动;2.在外周血管可能存在两种不同的5-HT 受体,一种主要分布在皮肤和肾脏,引起缩血管效应;另一种主要分布于骨胳肌和冠状血管,引起扩血管效应。     

狗静脉注射高渗溶液后的血流动力学分析

在15只戊巴比妥钠麻醉的开胸狗身上观察高渗溶液对血流动力学的影响,主要结果如下:1.静脉内注射50%葡萄糖溶液(3m1/kg,15s 内注毕),规律地引起心动徐缓、动脉血压降低、左心室(-dp/dt)减小、左心室 dp/dt 和心输出量增加,以及肾和股薄肌的血流阻力降低。25%甘露醇溶液具有类似作用。2.切断两侧颈迷走神经后,注射高渗溶液不再能诱发动脉低血压以及肾和股薄肌血流阻力的反射性降低,提示此类效应的传入通路主要为迷走神经。3.在切断迷走神经后注射高渗溶液,还使左心室 dp/dt 进一步增加,表明高渗溶液增强心肌收缩性。根据以上结果似可认为,静脉注射高渗溶液所致动脉血压降低,实质上反映着心输出量的增加不足以抵销外周阻力的减小。     

Antenna organization and evidence for the function of a new antenna pigment species in the green photosynthetic bacterium Chloroflexus aurantiacus

Whole cells and isolated chlorosomes (antenna complex) of the green photosynthetic bacterium Chloroflexus aurantiacus have been studied by absorption spectroscopy (77 K and room temperature), fluorescence spectroscopy, circular dichroism, linear dichroism and electron spin resonance spectroscopy. The chlorosome absorption spectrum has maxima at 450 (contributed by carotenoids and bacteriochlorophyll (BChl) a Soret), 742 (BChl c) and 792 nm (BChl a) with intensity ratios of 20:25. The fluorescence emission spectrum has peaks at 748 and 802 nm when excitation is into either the 742 or 450 nm absorption bands, respectively. Whole cells have fluorescence peaks identical to those in chlorosomes with the addition of a major peak observed at 867 nm. The CD spectrum of isolated chlorosomes has an asymmetric-derivative-shaped CD centered at 739 nm suggestive of exciton interaction at least on the level of dimers. Linear dichroism of oriented chlorosomes shows preferential absorption at 742 nm of light polarized parallel to the long axis of the chlorosome. This implies that the transition dipoles are also oriented more or less parallel to the long axis of the chlorosome. Treatment with ferricyanide results in the appearance of a 2.3 G wide ESR spectrum at g 2.002. Whole cells grown under different light conditions exhibit different fluorescence behavior when absorption is normalized at 742 nm. Cells grown under low light conditions have higher fluorescence intensity at 748 nm and lower intensity at 802 nm than cells grown under high light conditions. These results indicate that the BChl c in chlorosomes is highly organized, and transfers energy from BChl c (742 nm) to a connector of baseplate BChl B792 (BChl a) presumably located in the chlorosome baseplate adjacent to the cytoplasmic membrane.     

中国疫霉属异宗配合种的交配型

在疫霉属真菌中,很多种是重要的经济植物的病原菌,寄主范围广泛,包括乔木、灌木和各种农作物;为害性大,常带来严重的经济损失。本文主要研究疫霉异宗配合种的交配型。根据疫霉在纯培养和成对培养(dual culture)中产生有性器官的能力,疫霉属可分为同宗配合种和异宗配合种两大类群。异宗配合种的A~1交配型与同一种或其它种的A~2交配型进行成对培养时,可以形成有性器官。两个可亲合菌系配合而形成有性器官时,可能发生基因重组,其结果将使病原菌具有更强的生存能力、致病力以及更广泛的寄主范围。因此,研究疫霉两种不同的交配型的分布,不仅对认识病害的发生发展规律,进一步设计防治措施有着重要意义,而且对疫霉属的起源、演化和移栖也有着深远的理论意义。作者对收集到的7个异宗配合种:Phytophthora capsici,P.cinnamomi,P.citrophthora,P.colocasiae,P.infestans,P.nicotianae,P.palmivora的38个分离物进行了交配型的研究,测定工作使用澄清的Campbell蔬菜汁琼脂培养基(V8C),用于确定交配型的菌系有P.nicotianae var.parasitica A~1,P.nicotianae var.parasitica A~2,P.cinnamomi A~1,P.cinnamomi A~2,P.palmivora A~1,P.palmivora A~2.每个分离物分别与已知种的A~1和A~2两个菌系成对接种于同一V8C平板上,放入25℃温箱中培养,2周后在两个菌落的连线上检查有性器官的产生情况。实验结果表明,中国疫霉属异宗配合种的这些分离物的交配型与寄主或地理分布似无相关性,同一种植物上分离到的同种疫霉可以是A~1交配型,也可以为A~2交配型;同一地区可以出现两种交配型,不同地区又有相同的交配型。云南西双版纳橡胶园中的分离物(P.citrophthora,P.colocasiae,P.palmivora)都表现为中性。     

Gastrin-amidating enzyme in the porcine pituitary and antrum. Characterization of molecular forms and substrate specificity

As is the case with many other peptide hormones of the brain and intestine, the formation of biologically active gastrin from a glycine-extended processing intermediate occurs via the action of a peptidylglycyl alpha-amidating monooxygenase (PAM). The observation that gastrin exists primarily as unamidated precursors in the pituitary but as amidated gastrin in the antrum prompted this study to examine whether the amidating enzymes in the two organs were different in their characteristics. Amidating activity was quantified by measuring the conversion of glycine-extended tridecagastrin (G13-Gly) to amidated tridecagastrin and glycine-extended hexapancreatic polypeptide (PP6-Gly) to amidated hexapancreatic polypeptide by radio-immunoassay. Two molecular forms of amidating activity were identified in both the porcine antrum and pituitary. The first, PAM-A, had an apparent Mr of 51,000 and a net negative charge at pH 7.0, whereas PAM-B was smaller (Mr approximately 30,000) and had a net positive charge at pH 7.0. Both molecular forms were similar in their cofactor requirements (copper, ascorbic acid, and catalase) and pH optima in the antrum and pituitary. The Km was significantly lower and the Vmax higher for PP6-Gly than for G13-Gly in the pituitary and antrum. These data suggest that although there is no difference between antral and pituitary PAM, the selective affinity of PAM for certain substrates may provide a mechanism for the differential amidation of different hormones within a given tissue or cell.     

Biochemical and genetic studies on the function of, and relationship between, the PGI1- and CDC30-encoded phosphoglucose isomerases in Saccharomyces cerevisiae

Isoelectric focusing was used to compare the complement of phosphoglucose isomerase isoenzymes in a wild-type strain of Saccharomyces cerevisiae and in a strain with a deletion in the PGI1 structural gene. Deletion of the PGI1 gene did not result in the absence of the high-Km isoenzyme I but the low-Km isoenzyme II was absent. Hence, the isoenzymes must be the products of two genes. If PGI1 were the sole structural gene its deletion would result in the disappearance of both isoenzymes. After a temperature shift-up a cdc30-bearing strain had cell cycle arrested and contained only 8% of the polysaccharide in the wild-type. Phosphoglucose isomerase is required for the synthesis of fructose 6-phosphate (F6-P), a precursor of the cell wall components chitin and mannoprotein ('mannan'), which are a polysaccharide and contain polysaccharide, respectively. Since the cdc30 mutation confers a temperature-sensitive phosphoglucose isomerase, the likely explanation for cell cycle arrest caused by this mutation is that the defective phosphoglucose isomerase results in a reduction of F6-P and hence an inability to synthesize the mannan and chitin needed for cytokinesis and cell separation. Revertants of a pgi1-1 bearing strain were selected for their ability to grow on glucose at 25 degrees C and this yielded a number of different phenotypes. Amongst the isolates was a strain which had undergone an intragenic reversion at the pgi1 locus, designated pgi1-1,100. This mutation permits growth and cell division at 25 degrees C but results in cell cycle arrest at 36 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)     

The activity of a model heterologous protein in pep4-3 mutants of Saccharomyces cerevisiae

Summary The bacterial lacZ gene was introduced into two sibling strains of Saccharomyces cerevisiae, one a wild-type strain with normal proteinase activity and the other a pep4-3 mutant strain. The pep4-3 mutation resulted in 90% reduced activity of the four major vacuolar proteinases. By comparing the activity of the lacZ gene product (-galactosidase) in both strains the degradative effect of the major vacuolar proteinases on a heterologous protein was estimated. The mutant strain with reduced proteinase activity had higher -galactosidase activity under all the test conditions. In the most productive case the pep4-3 mutant had 55% higher -galactosidase activity than the wild-type. Batch cultures of the two strains were evaluated for growth characteristics. The strain with reduced proteinase activity grew to higher optical densities than the wild-type. Upon further examination it was found that not only were the optical densities of pep4-3 cultures greater but the cell numbers were much greater than expected due to the smaller size of pep4-3 cells. It is concluded that the strain lacking vacuolar proteinases maintained increased levels of -galactosidase and is physiologically as healthy as the wild-type.Offprint requests to: J. M. Wingfield