Rapid recycling of triose phosphates in oak stem tissue

We report the carbon-13 and oxygen-18 isotope ratios in cellulose from the early and late wood of pedunculate oak (Quercus robur L.). The δ¹³ C value of the early wood correlates best with that of the late wood of the previous year. The δ¹⁸O value of the early wood correlates best with that of the late wood of the same year. We suggest that a biochemical explanation of these data is that there is a rapid cycle between hexose monophosphates and triose phosphates in oak stem tissue during cellulose synthesis. Evidence in support of this explanation is provided by the intramolecular distribution of ¹⁴C in labelled fructose extracted from cores of wood that had been supplied with [1?¹⁴C]- and [6-¹⁴C]glucose.     

内源无机磷酸盐对叶绿体Mg~（2＋）－ATP酶功能的调节

用ＳＴＮ（含蔗糖,０．４ｍｏｌ／Ｌ;ＮａＣｌ,０．０１ｍｏｌ／Ｌ和Ｔｒｉｓ－ＨＣｌ,０．０２ｍｏｌ／Ｌ,ｐＨ７．４）提取的菠菜叶片叶绿体再用ＳＴＮ洗涤后,它的内源无机磷酸盐含量急剧减少,其Ｍｇ２＋－ＡＴＰ酶水解ＡＴＰ的能力明显下降。进一步研究表明：叶绿体的内源无机磷酸盐含量减少会使反映叶绿体类囊体膜内外△ｐＨ变化的９－氨基吖啶的荧光猝灭减少,并加速光激活态ＡＴＰ酶的暗失活。     

Sucrose metabolism and fruit growth in parthenocarpic vs seeded blueberry (Vaccinium ashei) fruits

Although fruit set and development are induced by applications of gibberellins, final fruit weight of gibberellin-induced parthenocarpic fruit is often less than that of pollinated fruit. We examined changes in the activities of sucrose-metabolizing enzymes and sugar accumulation in developing fruits of cultivated blueberry (Vaccinium ashei Reade) and their correlation with fruit growth upon pollination or exogenous applications of gibberellic acid (GA₃). The objective was to determine if differences in fruit growth could be attributed to differences in enzyme activities and subsequent sugar accumulation in fruits. The fruit development period of GA₃-treated fruits was 15 days longer than that of pollinated fruits. At maturity, GA₃-treated fruit accumulated an average of 180 mg dry weight while pollinated fruit accumulated 390 mg dry weight. Dry weight accumulation in nonpollinated fruits was negligible and these fruits abscised by 45 days after bloom (DAB). The total carbon (C) cost (dry weight C + respiratory C) for fruit development was 109 and 244 mg C fruit^-1 for GA₃-treated and pollinated fruits, respectively. Hexose concentration increased to 100 mg (g fresh weight)^-1 at ripening in both GA₃-treated and pollinated fruits. Nonpollinated fruits reached a maximum hexose concentration at 45 DAB. Sucrose phosphate synthase (EC 2.4.1.14) and sucrose synthase (EC 2.4.1.13) activities reached a maximum of ≤5.0 μmol (g fresh weight)^-1 h^-1 in both GA₃-treated and pollinated fruits. Soluble acid invertase (EC 3.2.1.26) activity increased to about 60 μmol (g fresh weight)^-1 h^-1 in both GA₃-treated and pollinated fruits at ripening, while in nonpollinated fruits, a maximum soluble acid invertase activity of 0.12 μmol (g fresh weight)^-1 h^-1 was measured at 24 DAB. Insoluble acid invertase activity declined during the early stages of fruit growth and remained relatively low throughout fruit development. Neutral invertase activity was low throughout development, increasing to 5 μmol (g fresh weight)^-1 h^-1 at ripening in GA₃-treated and pollinated fruits. Our studies demonstrate that blueberry fruit development does not appear to be limited by sucrose metabolizing enzyme activity and/or the ability to accumulate sugars in either GA₃-treated or pollinated fruits.     

Metabolic implications of stress-induced proline accumulation in plants

In many plants, free proline accumulates in response to the imposition of a wide range of biotic and abiotic stresses. Controversy has surrounded the extent to which this shift in nitrogen metabolism benefits plants under adverse environmental conditions. Most attempts to account for the phenomenon have focused on the ability of proline to mediate osmotic adjustment, stabilise subcellular structures and scavenge free radicals. However, often the cytoplasmic pool of free proline even after the imposition of stress is insufficient size to account for pronounced biophysical effects.Alternatively, selective preservation of this stress-induced response may relate to endpoints other than simply augmenting the cellular pool of free proline. Proline accumulation may reduce stress-induced cellular acidification or prime oxidative respiration to provide energy needed for recovery. High levels of proline synthesis during stress may maintain NAD(P)+/NAD(P)H ratios at values compatible with metabolism under normal conditions. Consideration of the cofactor preference of plant 1-pyrroline-5-carboxylate (P5C) reductase as well as the in vivo concentrations of the two pyridine nucleotide cofactors and their respective redox ratios suggests that even a small increase in proline biosynthesis might have a large impact on the level of reduction of the cellular NADP pool. The increased NADP+/NADPH ratio mediated by proline biosynthesis is likely to enhance activity of the oxidative pentose phosphate pathway. This would provide precursors to support the demand for increased secondary metabolite production during stress as well as nucleotide synthesis accompanying the accelerated rate of cell division upon relief from stress, when oxidation of proline is likely to provide an important energy source for ADP phosphorylation. Thus, the extreme sensitivity of the metabolic processes of proline synthesis and degradation themselves may be of benefit by regulating metabolic processes adversely affected by stress. This viewpoint is supported by consideration of other physiological phenomena not directly related to stress responses, but in which proline metabolism may also play a regulatory role.A mechanism is proposed whereby the interconversions of proline and P5C in different cell types and the associated transfer of redox potential between tissues may constitute a form of metabolic signalling within higher plants. Stress-related alterations in proline metabolism may impinge on systems of redox control of plant gene expression.     

Effectors ofd-[3H]aspartate release from rat cerebellum

The effect of aminooxyacetic acid (AOAA), NH₄ ⁺, phenylsuccinate (Phs), ketone bodies (KB) and glutamine (Gln), that might interfere with the biosynthesis of neurotransmitter glutamate on the K⁺-evoked Ca²⁺-dependent release ofd-[³H]aspartate from rat cerebellar slices was studied. Therefore slices were preincubated in a Krebs-Ringer-bicarbonate-glucose (KR) buffer, loaded withd-[³H]aspartate and superfused in the presence of Ca²⁺ or when Ca²⁺ was replaced by Mg²⁺ or in some cases by EGTA. AOAA, NH ₄ ⁺ and Phs increase the K⁺-evoked Ca²⁺-dependent release of radioactivity by 30%, 68% and 188% compared to the control respectively indicating that these agents are inhibitors of the K⁺-evoked Ca²⁺-dependent release of glutamate. KB and Gln had no effect on the Ca²⁺-dependent release of radioactivity. AOAA., NH ₄ ⁺ , Phs and KB but not Gln increase the total release of radioactivity by 43%, 69%, 139%, and 37% respectively. AOAA, NH ₄ ⁺ and KB but not Phs or Gln increase the Ca²⁺-independent release (Mg²⁺ replacing Ca²⁺) of radioactivity by 71%, 71% and 108% respectively. The present results indicate that in the cerebellum: 1) Neurotransmitter glutamate is mostly synthesized through the phosphate activated glutaminase (PAG) reaction 2) It is further supported that glutamate released in a Ca²⁺-dependent manner before entering its pool in the cytosol has to move into the mitochondrial matrix.     

Tryptophanase-catalysed degradation of D-tryptophan in highly concentrated diammonium hydrogen phosphate solution

Summary Tryptophanase is and is perfectly inert to D-tryptophan under ordinary conditions. However, activity that can degrade D-tryptophan into indole is observed when tryptophanase is in highly concentrated diammoniumhydrogen phosphate solution. The reaction has been so far unknown in tryptophanase metabolic pathways. Here we report the characteristic of the reaction. We also discuss its significance in relation to selection of an amino acid optical isomer from a racemic mixture.Abbreviations AP diammoniumhydrogen phosphate - TPase tryptophanase - L-Trp L-tryptophan - D-Trp D-tryptophan - PLP pyridoxal 5-phosphate     

The diverse world of coenzyme A binding proteins

Coenzyme A is involved in a number of important metabolic pathways. Recently the structures of several coenzyme A binding proteins have been determined. We compare in some detail the structures of seven different coenzyme A protein complexes. These seven proteins all have distinctly different folds.     

Factors determining rock phosphate solubilization by microorganisms isolated from soil

Forty two soil isolates (31 bacteria and 11 fungi) were studied for their ability to solubilize rock phosphate and calcium phosphate in culture medium. Eight bacteria and 8 fungi possessed solubilizing ability. Pseudomonas cepacia and Penicillium purpurogenum showed the highest activity. There was a correlation between final pH value and titratable acidity (r=–0.29 to –0.87) and between titratable acidity and soluble phosphate (r=0.22 to 0.99). Correlation values were functions of insoluble phosphate and of the group of microorganisms considered. A high correlation was observed between final pH and soluble phosphate only for the rock phosphates inoculated with the highest concentration of solubilizing bacteria (r=–0.73 to –0.98).     

Synthesis of an analogue of the lipoglycopeptide membrane intermediate I of peptidoglycan biosynthesis

-Dihydroheptaprenyl-pyrophosphoryl- N-acetylmuramoyl-L-Ala--D-Glu- meso-diaminopimeloyl(N-dansyl)-D-Ala-D-Ala ( 1), an analogue of lipid I ofpeptidoglycan biosynthesis, was synthesized from natural UDP-N-acetylmuramoyl-pentapeptide in three steps. Compound 1 was shown to be asubstrate for the MurG transferase from Escherichia coli, even in theabsence of membranes. When membranes were present, dansylated peptidoglycanwas also formed.