Effects of chemical composition on nitrogen mineralization from green manures of seven tropical leguminous trees

Green manures from seven tropical leguminous trees were incubated with soil to determine the rates and controls of net nitrogen release. Fresh green manure (leaves and succulent twigs) was mixed with moist soil and incubated in polyethylene bags. Net N mineralization from green manures was estimated by the accumulation of extractable ammonium and nitrate minus the accumulation in soil alone. Patterns of N mineralization were complex, differed among species, and at 12 weeks ranged from 10 to 65 percent of original green-manure N. Cumulative net N mineralization was negatively correlated with initial soluble polyphenol content in the early phases of decomposition (1 through 8 weeks) and with initial lignin content in later phases (4 through 12 weeks). Neither initial percent N nor lignin: N ratio were strongly correlated with N mineralization. The best chemical index of N release was the initial polyphenol: N ratio. This study confirms previous findings that N mineralization from tropical legumes is controlled more by soluble polyphenols than by lignin or N content.     

Nitrogen mineralization in acid sulfate soils

Summary Mineralization of soil nitrogen studies with two acid sulfate soils under anaerobic and aerobic incubation at 30°C for 2 weeks showed that the mineral N was released and accumulated entirely as NH ₄ ⁺ in both soils. Nitrification did not occur in either of the soils under conditions that stimulate nitrification. The acid sulfate soils studied release good amounts of mineralizable N, and, because of lack of nitrifying activity, denitrification may not be a serious problem in these soils.     

DDT inhibition of Ca-Mg ATPase from peripheral nerves and muscles of lobster, Homarus americanus

Sensitivity of CaMg ATPase from axonic plasma membrane (APM) and sarcoplasmic reticulum (SR) of lobster, $\text{Homarus}\text{,}\text{americanus}$, to DDT was studied. The CaMg ATPase found in SR with the high Ca²⁺ affinity is sensitive to DDT while the portion of ATPase related to the low Ca²⁺ affinity site is not inhibited by DDT. Also, DDT is more inhibitory against the CaMg ATPase prepared from APM than the one obtained from SR. The relationship between inhibition of the CaMg ATPase by DDT in the axonic nerve membrane and $\text{in}\text{,}\text{vivo}$ poisoning symptoms of the nervous system is discussed.     

A respiration-dependent primary sodium extrusion system functioning at alkaline pH in the marine bacterium Vibrioalginolyticus

The membrane potential generated at pH 8.5 by K⁺-depleted and Na⁺-loaded $\text{Vibrio}\text{alginolyticus}$ is not collapsed by proton conductors which, instead, induce the accumulation of protons in equilibrium with the membrane potential. The generation of such a membrane potential and the accumulation of protons are specific to Na⁺-loaded cells at alkaline pH and are dependent on respiration. Extrusion of Na⁺ at pH 8.5 occurs in the presence of proton conductors unless respiration is inhibited while it is abolished by proton conductors at acidic pH. The uptake of α-aminoisobutyric acid, which is driven by the Na⁺-electrochemical gradient, is observed even in the presence of proton conductors at pH 8.5 but not at acidic pH. We conclude that a respiration-dependent primary electrogenic Na⁺ extrusion system is functioning at alkaline pH to generate the proton conductor-insensitive membrane potential and Na⁺ chemical gradient.     

1-Butanol extracted proteolipid. Proton conducting properties

The 1-butanol extracted proteolipid from mitochondria was incorporated to liposomes. This proteolipid mediates the H⁺ transfer across the lipid bilayer in response to a negative charge produced by valinomycin and KCl. The process is sensitive to DCCD, but not to oligomycin. The flux of H⁺ depends on the concentration of proteolipid and the inhibition of this flux depends on the concentration of DCCD.     

Regulation of proton leakage from broken chloroplasts by CF0.

Measurements of proton translocation in CF₁-depleted, N, N′-dicyclohexylcarbodiimide-resealed broken chloroplasts were made under different light intensities. Kinetic analysis of the data shows that the outward leakage of accumulated protons through CF₀ is still dependent on light intensity with a first-order rate constant equal to mR₀, where R₀ is the initial rate of proton uptake which normally increases with light intensity and m is a characteristic constant which is independent of proton gradient and light intensity. Measurements of proton translocation in these modified chloroplasts cross-linked with glutaraldehyde under illumination and in the dark respectively suggest that the light-dependent proton leakage through CF₀ is regulated by conformation change in the membrane. It is proposed that the ovserved regulation of proton leakage through the CF₁.CF₀ complex in native chloroplasts is for optimizing the steady state synthesis of ATP under different light intensities.     

Urease catalysis and structure: X. Alternate bonding-site isozymes of jackbean urease

Three previously uncharacterized, nongenetic urease isozymes have been analyzed by sucrose density gradient sedimentation, gel electrophoresis, and chemical reactivity. The full complement of isozymes could be reliably generated by choosing appropriate levels of NaCl, pH, and ethylene glycol, and was stable for several days in dilute solution. The three forms of interest were found to be quaternary isomers of other isozymes, but differed from them qualitatively in their bonding sites, with disulfide bonds being substituted for noncovalent bonds. The separation of these isomer-pairs during sedimentation and electrophoresis cannot be readily explained by differences in size or charge, but must rather arise from a difference in shape. A simple two-dimensional model can provide the appropriate molecular architecture to satisfy these requirements: Only one of the two half-units in each α-urease molecule undergoes disulfide bonding during polymerization, and it does so with two adjacent molecules, thus producing asymmetric polymers from symmetric starting components.     

Resolution of cyclic AMP stimulated protein kinase from polymerization-purified brain microtubules.

Polymerization-deploymerization purified microtubules from mouse brain contain, in addition to tubulin, several minor proteins, including protein kinase activity. The protein kinase copurifies with microtubules in constant proportion to tubulin through two, three, or four cycles of polymerization; it can be resolved from tubulin by gel filtration chromatography and has an apparent molecular weight of 280,000. Its activity is stimulated 7-fold by cyclic AMP, and resembles the soluble brain protein kinase described by Miyamoto $\text{et al.}$ (1). The microtubule preparation serves as an endogenous substrate for this protein kinase; both 6S and 30S tubulin are substrates for phosphorylation to the extent of about 0.10 ± 0.05 moles/mole.     

秋冬季叶施N、Fe提高假俭草草坪抗寒性研究

在过渡性气候地区的假俭草草坪,宜在最低气温为12℃时(11月中、下旬)叶施Fe,最佳施用浓度为:单施Fe为0.6L/m²,N+Fe为4g/m² N+0.6L/m²Fe。秋冬季叶施Fe、N+Fe可提高草体内抗寒指标性物质的含量,叶施0.6L/m² Fe或4g/m² N+0.6L/m² Fe,可使草坪草体内脯氨酸、可溶性糖类含量及过氧化氢酶的活性分别提高25%、310%、180%和41%、182%、160%。叶施N+Fe处理的效果比单独施Fe的效果更好,施后草坪枯黄期比对照组推迟6~8d,半致死温度降低3~4℃。     

蝉花虫草活性成分的抗惊厥作用

本研究采用活性追踪的方法,逐步从人工培养蝉花虫草分离获得A（50%乙醇回流提取）、B（膜分离）、C（大孔树脂洗脱）和D（Sephadex LH20柱纯化）等4种样品,单一化合物D纯度为98.62%,鉴定为N6‐(2‐羟乙基)腺苷[N6‐(2‐hydroxyethyl)‐adenosine,HEA]。研究各样品对戊四唑（pentylenetetrazol,PTZ）诱导的小鼠惊厥模型的影响,以及选择性腺苷A1受体（AA1R）拮抗剂DPCPX或选择性腺苷A2A受体（AA2AR）拮抗剂ZM241385对HEA作用的影响,并采用苏木精-伊红（hematoxylin-eosin,HE）染色、免疫组化（immunohistochemical,IHC）染色和蛋白质免疫印迹（Western blot,WB）等技术进一步探究HEA抗惊厥作用的机制。结果表明,各样品（i.p.）均有抗惊厥活性,HEA（40–60mg/kg,i.p.）能显著延长惊厥小鼠的存活时间和降低死亡率,DPCPX（2mg/kg,i.p.）能够拮抗HEA的抗惊厥作用,而ZM241385无此作用;HE、IHC和WB的结果进一步揭示DPCPX显著降低HEA的作用。综上所述,蝉花虫草的HEA具有抗惊厥作用,并且可能通过激活腺苷A1受体而起作用。