Glutamate oxaloacetate transaminase isozymes of the Triticinae: dissociation and recombination of subunits

Summary A simple procedure has been developed for the dissociation of active molecules of glutamate oxaloacetate transaminase (GOT: E.C. 2.6.1.1) into protomers and for the reassociation of the subunits into active enzymes. Results of experiments in which the protomers of genetically controlled electrophoretic variants of GOT of Triticum aestivum and of several related species were dissociated and recombined in crude tissue extracts and in partially purified preparations support the hypothesis that the enzyme exists functionally as a dimer in the Triticinae.This paper is Technical Article No. 13157 of the Texas Agricultural Experiment Station.     

Lactate dehydrogenase isozymes in the genus Channa: Species-specific patterns

The lactate dehydrogenase isozyme system for five Channa species (snakehead fish) have been examined by means of polyacrylamide gel electrophoresis. The pattern and distribution of the LDH isozymes in all these species are found to be species-specific with a reversed relative mobility of the A and B subunits as compared to most of the other vertebrates. In addition to these two subunits, an eye-specific LDH E isozyme has also been detected in these species.     

Dissociation of mitochondrial malate dehydrogenase into active soluble subunits

Gel exclusion chromatographic studies demonstrate that cytosolic and mitochondrial malate dehydrogenases (cMDH and mMDH) dissociate into subunits in the presence of 0.1% of the non-ionic detergent Triton X-100 (TX-100). The presence of cofactor and catalytically competent cofactor-substrate pairs does not protect mMDH against this dissociation. In contrast, cMDH dimers resist dissociation in the presence of either addition. Since steady state kinetic studies indicate both enzymes are fully active in the presence of 0.1% TX-100, we conclude that quaternary structure is not a kinetically important feature of mMDH structure and cooperativity does not account for mMDH kinetic anomalies. In contrast, cooperativity is a reasonable explanation for cMDH kinetic properties even in the presence of 0.1% TX-100, since this enzyme's subunits associate in the presence of active site ligands. The existence of fully active mMDH subunits raises the possibility that this species rather than the dimer may be a constituent of proposed multi-enzyme complexes of the mitochondrion. Preliminary chromatographic experiments involving gently disrupted mitochondria have found MDH activity in differently sized complexes, all with molecular weights larger than the mMDH dimer but smaller than complexes anticipated for multi-enzyme complexes involving other enzymes and the mMDH dimer.     

D-乳酸生产菌菊糖芽孢乳杆菌来源的D-乳酸脱氢酶同工酶

【目的】菊糖芽孢乳杆菌(Sporolactobacillus inulinus)作为典型的同型发酵产D-乳酸的优势菌株,能够高效生产高纯度的D-乳酸。该菌株发酵受到多方面环境因素影响。糖代谢的关键酶例如葡萄糖激酶、磷酸果糖激酶、丙酮酸激酶以及乳酸脱氢酶均为由葡萄糖代谢成为乳酸的关键酶,该菌中相关代谢酶的研究是发酵调控至关重要的基础。分析S.inulinus的基因组表明有3个推测为D-乳酸脱氢酶的基因,其中已有报道研究了1个双功能蛋白[bifunctional protein(BP)]。本研究分别克隆并解析了另2个D-乳酸脱氢酶同工酶的性质。【方法】本研究以S.inulinus Y2-8基因组DNA为模板,克隆得到2个D-ldh基因(dldh、dhdh),经测序分别为D-乳酸脱氢酶[D-lactic acid dehydrogenase(DLDH)]和D-羟基酸脱氢酶[D-isomer specific 2-hydroxyacid dehydrogenase(DHDH)]的基因。构建的重组菌表达蛋白DLDH,DHDH均具有催化丙酮酸生成D-乳酸的功能。【结果】重组菌表达的蛋白经镍柱亲和层析达到电泳纯。SDS-PAGE分析表明DLDH的表观分子量为37 k Da,DHDH的表观分子量为39 k Da。此外,DLDH以丙酮酸为底物时Km值为(0.58±0.04)mmol/L,对底物有较高的亲和力,最适反应温度为35°C,最适p H为6.5;而DHDH以丙酮酸为底物时Km值为(1.70±0.08)mmol/L最适反应温度为30°C,最适p H为7.5。另有报道的BP以丙酮酸为底物时Km值为(3.40±0.02)mmol/L,最适反应温度为30°C,最适p H为5.5。【结论】根据对底物丙酮酸的亲和力,最适温度及最适p H,推测DLDH是乳酸发酵中产D-乳酸的主导催化剂。结合相关酶学性质的分析可为今后的发酵调控提供理论依据。     

Alcohol dehydrogenase isozymes inGossypium hirsutum and its putative diploid progenitors: The biochemical consequences of enzyme multiplicity

Electrophoretic variation in alcohol dehydrogenase (ADH) was examined in tetraploidGossypium hirsutum and its putative diploid progenitorsG. ramondii, G. herbaceum, and a close relative,G. arboreum. All the diploids had three isozymes, while strains of the tetraploidG. hirsutum had either 4 or 6. Each isozyme was eluted from starch gels and significant differences in activity were noted between several of the isozymes relative to pH, substrate, temperature and salinity. This suggests that an increase in enzyme heterozygosity can result in higher levels of developmental homeostasis, but it depends on the isozyme alleles involved. Michigan Agricultural Experiment Station Journal Article No. 10379.     

Alcohol dehydrogenase in Arabidopsis: analysis of the induction phenomenon in plantlets and tissue cultures

Summary Alcohol dehydrogenase (ADH) activity is expressed in Arabidopsis seeds and tissue cultures. During the germination process, ADH activity declines rapidly and is no longer detectable in 9- to 10-day-old seedlings. The synthesis of ADH could be demonstrated in seedlings submitted to anaerobiosis by ³⁵S-methionine incorporation studies.Callus, induced from seeds or leaves on a 2,4-dichlorophenoxyacetic acid (2,4-D)-containing medium, and cell suspension cultures are characterized by a high level of ADH activity. The incorporation of ³⁵S-methionine and two-dimensional electrophoresis indicated that ADH induction was due to de novo synthesis of the polypeptides. In vitro translation of total poly (A)⁺-RNA from seedlings and callus showed that only callus mRNA was able to direct the synthesis of ADH polypeptides. This demonstrates the de novo synthesis of ADH mRNA during callus induction.Northern blot hybridization, using in vitro labelled ADH1-F DNA from maize as a probe, revealed sequence homology at the mRNA level between Arabidopsis and maize.Dedicated to professor Georg Melchers to celebrate his 50-year association with the journal     

Alcohol dehydrogenase isozymes in grain sorghum (Sorghum bicolor): Evidence for a gene duplication

Two sets of alcohol dehydrogenase (ADH) bands are regularly observed in grain sorghum (Sorghum bicolor): set I is a permanent triplet; set II is variable, as either two or three bands. A faint set III is detected only when extracts from seeds subjected to anerobiosis are run in neutralpH gels. Dissociation-reassociation experiments reveal that the central band of the set I triplet is a heterodimer of the other two. Full-sib progeny analysis from selfed plants shows that the set II bands are doublets, with heterozygotes having only three apparent bands instead of four because of the similar mobilities of the fast-migrating isozyme specified by the slow allele and the slow isozyme specified by the fast allele. We propose a three-locus model as the best explanation of these patterns. Set I consists of the products of two loci and their intergenic heterodimer. Set III is specified by a third locus. Set II isozymes are the intergenic heterodimers of the two set I loci and the set III locus. This explanation is similar to that of Schwartz and Freeling for maize but suggests that the evolution ofSorghum includes a gene duplication of the homologue of theAdh-1 locus inZea. Supported by USDA Grant 59-2063-01522 to NCE and KWF.     

Reducing the allelopathic effect of Partheniumhysterophorus L. on wheat (Triticumaestivum L.) by Pseudomonasputida

The present study evaluates the role of Pseudomonas putida NBRIC19 in alleviating biotic stress of Parthenium hysterophorus (Parthenium) in Triticum aestivum. Due to presence of Parthenium there was 43.76, 53.08 and 78.65% inhibition in root length, shoot length and dry weight of wheat respectively. This inhibition was recovered when P. putida NBRIC19 treatment resulted in 52.29, 28.73 and 76.31% increase in root length, shoot length and dry weight respectively as compared to control. P. putida NBRIC19 was able to form more biofilm under toxic environment of allelochemicals and enhanced expression of stress responsive genes in wheat. Inoculated wheat plants showed lower activity of catalase and ascorbate peroxidase under biotic stress of Parthenium indicating that inoculated plants felt less stress as compared to uninoculated plants. Microbial community structure in bacterized and nonbacterized wheat rhizosphere in presence and absence of Parthenium, was investigated using Biolog. There was significant increase in microbial diversity in P. putida NBRIC19 bacterized wheat rhizosphere. Functional microbial diversity revealed that P. putida NBRIC19 had shifted the microflora in such a manner that utilization of phytotoxic allelochemicals increased to lessen its toxic effect and finally it resulted in better growth of wheat in presence of Parthenium. Principal component analysis showed that microbial community function in nonbacterized wheat rhizosphere in presence (WPC) and absence (WC) of Parthenium is totally different from each other but due to P. putida NBRIC19 treatment there was close clustering of WPT and WT indicating a total shift in microbial community structure.     

Genetic recombination in Bacillus subtilis 168: effect of recN, recF, recH and addAB mutations on DNA repair and recombination

A recN ^– (recN1) strain of Bacillus subtilis was constructed. The effects of this and recF, recH and addAB mutations on recombination proficiency were tested. Mutations in the recN, recF recH and addAB genes, when present in an otherwise Rec⁺ B. subtilis strain, did not affect genetic exchange. Strains carrying different combinations of mutations in these genes were constructed and examined for their sensitivity to 4-nitroquinoline1-oxide (4NQO) and recombination proficiency. The recH mutation did not affect the 4NQO sensitivity of recN and recF cells and it only marginally affected that of addA addB cells. However, it reduced genetic recombination in these cells 10²- to 10⁴-fold. The addA addB mutations increased the 4NQO sensitivity of recF and recN cells, but completely blocked genetic recombination of recF cells and marginally affected recombination in recN cells. The recN mutation did not affect the recombinational capacity of recF cells. These data indicate that the recN gene product is required for, DNA repair and recombination and that the recF, recH and addAB genes provide overlapping activities that compensate for the effects of single mutants proficiency. We proposed that the recF, recH, recB and addA gene products define four different epistatic groups.     

Map position of Aldox (Aldehyde-oxidase) and Adh (Alcohol dehydrogenase) loci on autosome II of Musca domestica L.

The Aldox and Adh structural loci of Musca domestica L. belong to autosome II. They code for the enzymes aldehyde oxidase and alcohol dehydrogenase. Both these enzymes have allelic variants with specific electrophoretic mobility, which, on cellogel, are seen as single bands. The Aldox and Adh loci encompass a large map interval, which includes the morphological markers ar, cm, and car. The recombination frequencies between these five loci indicate the alignment Aldox-ar-cm-car-Adh.

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Localisation chez Musca domestica L. des gènes Aldox et Adh codant les enzymes ald\;ehyde oxydase (AO) et alcool déshydrogénase (ADH)

Résumé Chez la mouche, les enzymes AO et ADH, observées par électrophorèse sur cellogel, présentent toutes 2 des formes alléliques exprimées par des bandes ayant une mobilité anodique propre.Les gènes structuraux Aldox et Adh, codant ces formes, sont liés entre eux et situés sur le chromosome 2. Ils se recombinent avec une fréquence élevée d'interchange; ils sont donc séparés par un intervalle important dans lequel sont compris les caractères visibles ar, cm, car. La fréquence des recombinaisons entre caractères visibles et gènes enzymatiques indique l'ordre suivant sur ce segment du deuxième chromosome de la mouche: Aldox, ar, cm, car, Adh.

     

Dissociation of mitochondrial malate dehydrogenase

The kinetics of the dissociation reaction under acidic conditions of the dimeric pig and chicken mitochondrial malate dehydrogenases (EC 1.1.1.37) have been studied. The dissociation of the pig enzyme is completely reversible. The pK for dissociation determined by light-scattering measurements agrees within experimental error with the pK value of 5.25 measured for a tyrosine-carboxylate pair. The rate constants for the dissociation reaction and for the protonation process of this tyrosine are in close agreement. Thus, the tyrosine-carboxylate pair can be used as indicator of the dissociation reaction. The dissociation of the chicken enzyme proceeds around pH 4.5 at a much lower rate. A true equilibrium between dimer and monomers is not found, since the monomer gradually unfolds at this pH. The monomers of both enzymes, pig and chicken mitochondrial malate dehydrogenase, show the same stability towards acid. The difference in stability of the dimeric forms, therefore, must be due to an altered subunit contact area.