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1. The pH in the stroma and in the thylakoid space has been measured in a number of chloroplast preparations in the dark and in the light at 20 °C. Illumination causes a decrease of the pH in the thylakoid space by 1.5 and an increase of the pH in the stroma by almost 1 pH unit.2. CO2 fixation is shown to be strongly dependent on the pH in the stroma. The pH optimum was 8.1, with almost zero activity below pH 7.3. Phosphoglycerate reduction, which is a partial reaction of CO2 fixation, shows very little pH dependency.3. Low concentrations of the uncoupler m-chlorocarbonylcyanide phenylhydrazone (CCCP) inhibit CO2 fixation without affecting phosophoglycerate reduction. This inhibition of CO2 fixation appears to be caused by reversal of light induced alkalisation in the stroma by CCCP.4. Methylamine has a very different effect compared to CCCP. Increasing concentrations of methylamine inhibit CO2 fixation and phosphoglycerate reduction to the same extent. The light induced alkalisation of the stroma appears not to be significantly inhibited by methylamine, but the protons in the thylakoid space are neutralized. The inhibition of CO2 fixation by higher concentrations of methylamine is explained by an inhibition of photophosphorylation. It appears that methylamine does not abolish proton transport.5. It is shown that intact chloroplasts are able to fix CO2 in the dark, yielding 3-phosphoglycerate. This requires the addition of dihydroxyacetone phosphate as precursor of ribulosemonophosphate and also to supply ATP, and the addition of oxaloacetate for reoxidation of the NADPH in the stroma.6. Dark CO2 fixation in the presence of dihydroxyacetone phosphate and oxaloacetate has the same pH dependency as CO2 fixation in the light. This demonstrates that CO2 fixation in the dark is not possible, unless the pH in the medium is artificially raised to pH 8.8.7. It is shown that pH changes occurring in the stroma after illumination are sufficient to switch CO2 fixation from zero to maximal activity. This offers a mechanism for light control of CO2 fixation, avoiding wasteful CO2 fixation in the dark. 相似文献
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Studies of the kinetics of association and dissociation of the formycin nucleotides FTP and FDP with CF1 were carried out using the enhancement of formycin fluorescence. The protein used, derived from lettuce chloroplasts by chloroform induced release, contains only 4 types of subunit and has a molecular weight of 280 000.In the presence of 1.25 mM MgCl2, 1 mol of ATP or FTP is bound to the latent enzyme, with Kd = 10?7 or 2 · 10?7, respectively. The fluorescence emission (λmax 340 nm) of FTP is enhanced 3-fold upon binding, and polarization of fluorescence is markedly increased. The fluorescence changes have been used to follow FTP binding, which behaves as a bimolecular process with K1 = 2.4 · 104 M?1 · s?1. FTP is displaced by ATP in a process apparently involving unimolecular dissociation of FTP with k?1 = 3 · 10?3 s?1. The ratio of rates is comparable to the equilibrium constant and no additional steps have been observed.The protein has 3 sites for ADP binding. Rates of ADP binding are similar in magnitude to those for FTP. ADP and ATP sites are at least partly competitive with one another.The kinetics of nucleotide binding are strikingly altered upon activation of the protein as an ATPase. The rate of FTP binding increases to at least 106 M?1 · s?1. This suggests that activation involves lowering of the kinetic barriers to substrate and product binding-dissociation and has implications for the mechanism of energy transduction in photophosphorylation. 相似文献
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A cDNA of Chlamydomonas reinhardtii encoding a plastidial homogentisate prenyltransferase was identified. Functional expression studies in Escherichia coli revealed that the enzyme possessed properties similar to the prenyltransferase of Arabidopsis thaliana encoded by At3g11950 but different from the phytyltransferases of A. thaliana and Synechocystis. Unlike the phytyltransferases, the C. reinhardtii and the respective A. thaliana enzyme showed highest activities with solanesyl diphosphate, but were hardly active with phytyl diphosphate. Hence, these data provide evidence that the latter represent homogentisate solanesyltransferases involved in plastoquinone-9 biosynthesis. Overexpression of At3g11950 in A. thaliana, however, suggests that the solanesyltransferase can affect tocopherol biosynthesis as well. 相似文献
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H D Hoberman 《Biochemical and biophysical research communications》1979,90(3):764-768
5-deoxy-D-xylulose-1-phosphate, which is formed in human erythrocytes from added acetaldehyde and endogenous dihydroxyacetone phosphate, reacts with hemoglobin Ao to form an adduct that is stable to repeated precipitation by trichloracetic acid and to prolonged dialysis against dilute phosphate buffer. Formation of this hemoglobin derivative in individuals who consume alcohol would serve to integrate the blood acetaldehyde concentration and thereby reflect a dose-time record of alcohol consumption. 相似文献
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通过比较6株酵母细胞转化1,6-二磷酸果糖的结果,确定酿造酵母Y162作为转化菌株,对其菌株的培养方法,底物反应额的组成及反应条件进行了详细的考察,在最适条件下:pH6.5,蔗糖8%,NaH2PO45%,MgCl2·6H2O0.1%,甲苯4.0%,氯丙嗪0.2%,反应时间为8-10h,湿菌体与反应液的比例为1:4,反应液中FDP的产量可达12.1mg/ml。 相似文献
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张国利曾湘良刘芳朱勇 《现代生物医学进展》2012,12(12):2340-2341
目的:探讨血浆中D-二聚体、C-反应蛋白及FDP比值在急性脑梗死中应用价值,为临床诊断提供指导。方法:抽取我院于2010年1月至2011年1月收治的30名急性脑梗死患者编为实验组。30名陈旧性脑梗死患者编为对照组。检测血浆中的D-二聚体、C-反应蛋白、FDP及其相互之间比值。结果:两组相比,实验组血浆D-二聚体、C-反应蛋白、FDP均与对照组差异无统计学意义(P>0.05);两组相比,实验组D-二聚体/FDP,C-反应蛋白/FDP均高于对照组,差异有统计学意义(P<0.05)。结论:急性和陈旧性脑梗死患者血浆中单独比较D-二聚体、C-反应蛋白、FDP差异均不明显,但D-二聚体/FDP,C-反应蛋白/FDP的阳性检出率较高,对临床有一定的指导意义。 相似文献
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