Formation of Desacetylcephalosporin C in Cephalosporin C Fermentation

The origin of desacetylcephalosporin C in cephalosporin C fermentation broths was investigated. Esterase activity was detected in cell-free extracts of Cephalosporium acremonium, but these extracts failed to deesterify cephalosporin C. When cephalosporin C was added to sterile and inoculated fermentation media, the antibiotic decayed at nearly identical rates. The formation of desacetylcephalosporin C during the fermentation was measured by quantitative chromatography and by the incorporation of valine-1-(14)C into the molecule. The rate constants obtained from the results of these experiments were equivalent to those for the decay of cephalosporin C in sterile and inoculated media. The data demonstrate that desacetylcephalosporin C is produced by nonenzymatic hydrolysis of cephalosporin C.     

Protein kinase C isotypes in C. elegans

The protein kinase C (PKC) family, consisting of multiple isotypes, plays a major role in cellular signaling. In the nematode Caenorhabditis elegans, four pkc genes, tpa-1, pkc-1, pkc-2 and pkc-3, have been identified and investigated. Molecular analysis of tpa-1, pkc-1, and pkc-2 has shown that each gene encodes multiple PKC isoforms with different expression patterns. One of the tpa-1 isoforms, which is expressed in vulval cells, is found to play a role in nicotine-induced adaptation. The expression of pkc-1 seems to be specific to neurons, while that of pkc-2 is detected in several types of cells including neurons and muscle cells. An aPKC member encoded by pkc-3 has been shown to play an essential role in establishing the polarity of the zygote. Recent studies have revealed that the mechanism of polarity establishment mediated by aPKC is evolutionarily conserved in diverse organisms from nematodes to mammals. C. elegans provides an excellent model system for molecular dissection of the cellular signaling pathways involving PKC.     

贺谈老百岁华诞

谈家桢教授是国际著名遗传学家,我国现代遗传学的奠基人之一,他也是一位卓越的教育家和社会活动家。 1909年9月15日,谈家桢先生出生于浙江宁波。他就读于苏州东吴大学,1930年获理学学士学位。随后赴北京燕京大学攻读硕士学位,导师是我国现代遗传学奠基人之一的李汝祺教授,1932年获硕士学位。经导师推荐,谈家桢先生赴美国深造,师从当代遗传学宗师摩尔根,在遗传学家杜布赞斯基的指导下完成博士研究生学业,于1936年获美国加州理工学院哲学博士学位。     

Co-function of C3-and C4-photosynthetic pathways in C3, C4 and C3-C4 intermediate Flaveria species

The potential for C₄ photosynthesis was investigated in five C₃-C₄ intermediate species, one C₃ species, and one C₄ species in the genus Flaveria, using ¹⁴CO₂ pulse-¹²CO₂ chase techniques and quantum-yield measurements. All five intermediate species were capable of incorporating ¹⁴CO₂ into the C₄ acids malate and aspartate, following an 8-s pulse. The proportion of ¹⁴C label in these C₄ products ranged from 50–55% to 20–26% in the C₃-C₄ intermediates F. floridana Johnston and F. linearis Lag. respectively. All of the intermediate species incorporated as much, or more, ¹⁴CO₂ into aspartate as into malate. Generally, about 5–15% of the initial label in these species appeared as other organic acids. There was variation in the capacity for C₄ photosynthesis among the intermediate species based on the apparent rate of conversion of ¹⁴C label from the C₄ cycle to the C₃ cycle. In intermediate species such as F. pubescens Rydb., F. ramosissima Klatt., and F. floridana we observed a substantial decrease in label of C₄-cycle products and an increase in percentage label in C₃-cycle products during chase periods with ¹²CO₂, although the rate of change was slower than in the C₄ species, F. palmeri. In these C₃-C₄ intermediates both sucrose and fumarate were predominant products after a 20-min chase period. In the C₃-C₄ intermediates, F. anomala Robinson and f. linearis we observed no significant decrease in the label of C₄-cycle products during a 3-min chase period and a slow turnover during a 20-min chase, indicating a lower level of functional integration between the C₄ and C₃ cycles in these species, relative to the other intermediates. Although F. cronquistii Powell was previously identified as a C₃ species, 7–18% of the initial label was in malate+aspartate. However, only 40–50% of this label was in the C-4 position, indicating C₄-acid formation as secondary products of photosynthesis in F. cronquistii. In 21% O₂, the absorbed quantum yields for CO₂ uptake (in mol CO₂·[mol quanta]^-1) averaged 0.053 in F. cronquistii (C₃), 0.051 in F. trinervia (Spreng.) Mohr (C₄), 0.052 in F. ramosissima (C₃-C₄), 0.051 in F. anomala (C₃-C₄), 0.050 in F. linearis (C₃-C₄), 0.046 in F. floridana (C₃-C₄), and 0.044 in F. pubescens (C₃-C₄). In 2% O₂ an enhancement of the quantum yield was observed in all of the C₃-C₄ intermediate species, ranging from 21% in F. ramosissima to 43% in F. pubescens. In all intermediates the quantum yields in 2% O₂ were intermediate in value to the C₃ and C₄ species, indicating a co-function of the C₃ and C₄ cycles in CO₂ assimilation. The low quantum-yield values for F. pubescens and F. floridana in 21% O₂ presumably reflect an ineffcient transfer of carbon from the C₄ to the C₃ cycle. The response of the quantum yield to four increasing O₂ concentrations (2–35%) showed lower levels of O₂ inhibition in the C₃-C₄ intermediate F. ramosissima, relative to the C₃ species. This indicates that the co-function of the C₃ and C₄ cycles in this intermediate species leads to an increased CO₂ concentration at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase and a concomitant decrease in the competitive inhibition by O₂.Abbreviations PEP phosphoenolpyruvate - PGA 3-phosphoglycerate - RuBP ribulose-1,5-bisphosphate     

Mitochondrial calcium oscillations in C2C12 myotubes

Mitochondrial Ca(2+) concentration ([Ca(2+)](m)) was monitored in C2C12 skeletal muscle cells stably expressing the Ca(2+)-sensitive photoprotein aequorin targeted to mitochondria. In myotubes, KCl-induced depolarization caused a peak of 3.03 +/- 0.14 micrometer [Ca(2+)](m) followed by an oscillatory second phase (5.1 +/- 0.1 per min). Chelation of extracellular Ca(2+) or blockade of the voltage-operated Ca(2+) channel attenuated both phases of the KCl response. The inhibitor of the sarcoplasmic reticulum Ca(2+)-ATPase, cyclopiazonic acid, reduced the amplitude of the KCl-induced [Ca(2+)](m) peak and prevented the oscillations, suggesting that these were generated intracellularly. No such [Ca(2+)](m) oscillations occurred with the nicotinic agonist carbachol, cyclopiazonic acid alone, or the purinergic agonist ATP. In contrast, caffeine produced an oscillatory behavior, indicating a role of ryanodine receptors as mediators of the oscillations. The [Ca(2+)](m) response was desensitized when cells were exposed to two consecutive challenges with KCl separated by a 5-min wash, whereas a second pulse of carbachol potentiated [Ca(2+)](m), indicating differences in intracellular Ca(2+) redistribution. Cross-desensitization between KCl and carbachol and cross-potentiation between carbachol and KCl were observed. These results suggest that close contacts between mitochondria and sarcoplasmic reticulum exist permitting Ca(2+) exchanges during KCl depolarization. These newly demonstrated dynamic changes in [Ca(2+)](m) in stimulated skeletal muscle cells might contribute to the understanding of physiological and pathological processes in muscular disorders.     

Oxidation of C1-compounds in Pseudomonas C.

Extracts of Pseudomonas C grown on methanol as a sole carbon and energy source contain a methanol dehydrogenase activity which can be coupled to phenazine methosulfate. This enzyme catalyzes two reactions namely the conversion of methanol to formaldehyde (phenazine methosulfate coupled) and the oxidation of formaldehyde to formate (2,6-dichloroindophenol-coupled). Activities of glutathione-dependent formaldehyde dehydrogenase (NAD+) and formate dehydrogenase (NAD+) were also detected in the extracts. The addition of D-ribulose 5-phosphate to the reaction mixtures caused a marked increase in the formaldehyde-dependent reduction of NAD+ or NADP+. In addition, the oxidation of [14C]formaldehyde to CO2, by extracts of Pseudomonas C, increased when D-ribulose 5-phosphate was present in the assay mixtures. The amount of radioactivity found in CO2, was 6;8-times higher when extracts of methanol-grown Pseudomonas C were incubated for a short period of time with [1-14C]glucose 6-phosphate than with [U-14C]glucose 6-phosphate. These data, and the presence of high specific activities of hexulose phosphate synthase, phosphoglucoisomerase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase indicate that in methanol-grown Pseudomonas C, formaldehyde carbon is oxidized to CO2 both via a cyclic pathway which includes the enzymes mentioned and via formate as an oxidation intermediate, with the former predominant.     

C3 and C6 complement types in schizophrenia

C3 and C6 complement types were studied in schizophrenic patients and controls. The distributions of the three common C3 types (F, FS and S) among the patients was significantly different from that in the controls (p less than 0.005) and the frequency of the C3F gene was significantly increased (p less than 0.0005) among the patients. There were no significant differences in C6 gene or phenotype frequencies between patient and controls.     

C3植物中C4途径的研究进展

综述了C3植物中C4途径的发现及研究现状;阐述了C3植物中C4途径的几种作用机理;根据C3植物中C4途径的存在,探讨了改造C3植物的遗传特性;并展望了这一领域的研究前景。     

Genetics of complement C4. Two homoduplication haplotypes C4S C4S and C4F C4F in a family

Summary A family in which two homoduplicated C4 haplotypes (or supergenes) segregate is described. One haplotype C4F ^* 3 C4F ^*2.2 is composed of two C4F alleles and the other C4S ^* 5.1 C4S ^*1 of two C4S alleles. The C4F duplication haplotype is a partial inhibitor of the Rodgers antigen, and judged from our family and population material, it seems to be rather frequent and associated with HLAB ^*35, Bf ^* F, and HLAD/DR ^*1. The C4S duplication haplotype is Rg(a-) and is not identified in individuals without another S, Ch(a+) variant.This work was supported by grant No 12-1727 from the Danish Medical Research Council     

C3和C4植物的氮素利用机制

提高植物的氮素利用效率(NUE)不仅有利于保障全球粮食安全, 也是实现农业可持续发展的重要途径。近半个世纪以来, 植物氮素利用机理研究已取得重要进展, 但NUE的调控机制仍不明确, NUE的提高仍然十分有限。高等植物集光合碳素同化和氮素同化于一体, 只有碳氮代谢相互协调, 才能维持植物体内的碳氮平衡, 保证植物正常生长发育。由于C₃和C₄植物的光合氮素利用率(PNUE)存在差异, 对氮素的利用效率也会存在差异。为了更有效地提高作物的NUE, 须更全面地了解C₃和C₄植物对氮素吸收、转运、同化和信号转导等关键因子的功能和调控机制。此外, 面对大气CO₂浓度增高和全球气候变暖条件下的植物碳氮同化及其机理的研究也不容忽视。该文综述了C₃和C₄植物氮素利用关键因素的差异及其调控机制, 并对提高C₃禾本科作物氮素利用效率的遗传改良途径进行了展望。     

C3, BF and C4 polymorphisms in Tunisians

The C3, BF, C4A and C4B polymorphisms were studied in a Tunisian population sample. The allelic frequencies for C3 were S = 0.844 and F = 0.148, and for BF, S = 0.535, F = 0.331, SO7 = 0.075 and F1 = 0.041. The most frequent C4 alleles were A3 and B1 followed in a decreasing order by A2, B2 and the A and B null alleles. The results indicate that the Tunisian population is intermediate between the Caucasian and Arab populations with some trace admixture of African Blacks.     

Short-patch correction of C/C mismatches in human cells

We examined whether the human nucleotide excision repair complex, which is specialized on the removal of bulky DNA adducts, also displays a correcting activity on base mismatches. The cytosine/cytosine (C/C) lesion was used as a model substrate to monitor the correction of base mismatches in human cells. Fibroblasts with different repair capabilities were transfected with shuttle vectors that contain a site-directed C/C mismatch in the replication origin, accompanied by an additional C/C mismatch in one of the flanking sequences that are not essential for replication. Analysis of the vector progeny obtained from these doubly modified substrates revealed that C/C mismatches were eliminated before DNA synthesis not only in the repair-proficient background, but also when the target cells carried a genetic defect in long-patch mismatch repair, in nucleotide excision repair, or when both pathways were deleted. Furthermore, cells deficient for long-patch mismatch repair as well as a cell line that combines mismatch and nucleotide excision repair defects were able to correct multiple C/C mispairs, placed at distances of 21–44 nt, in an independent manner, such that the removal of each lesion led to individual repair patches. These results support the existence of a concurrent short-patch mechanism that rectifies C/C mismatches.     

C4-derived soil organic carbon decomposes faster than its C3 counterpart in mixed C3/C4 soils

The large difference in the degree of discrimination of stable carbon isotopes between C3 and C4 plants is widely exploited in global change and carbon cycle research, often with the assumption that carbon retains the carbon isotopic signature of its photosynthetic pathway during later stages of decomposition in soil and sediments. We applied long-term incubation experiments and natural ¹³C-labelling of C3 and C4-derived soil organic carbon (SOC) collected from across major environmental gradients in Australia to elucidate a significant difference in the rate of decomposition of C3- and C4-derived SOC. We find that the active pool of SOC (ASOC) derived from C4 plants decomposes at over twice the rate of the total pool of ASOC. As a result, the proportion of C4 photosynthesis represented in the heterotrophic CO₂ flux from soil must be over twice the proportional representation of C4-derived biomass in SOC. This observation has significant implications for much carbon cycle research that exploits the carbon isotopic difference in these two photosynthetic pathways.     

C/C ratio changes in crassulacean Acid metabolism plants

¹³C/¹²C ratios have been found in totally combusted leaves of Crassulacean acid metabolism plants to range from −14 to −33 δ ¹³C‰ compared with a limestone standard. Crassulacean acid metabolism plants apparently utilize both ribulose-1, 5-diphosphate carboxylase and phosphoenolpyruvate carboxylase to assimilate atmospheric CO₂ and, depending on environmental conditions, have ¹³C/¹²C ratios indicative of either carboxylase or to any intermediate value. The degree of discrimination against ¹³C and the resultant ¹³C/¹²C ratio from the photosynthetically fixed CO₂ is influenced by environmental conditions and is not a specific and fixed characteristic of a Crassulacean acid metabolism plant. Certain Crassulacean acid metabolism plants may shift their ratios as much as 17 δ ¹³C‰ in specific environments.