Mitochondrial malate dehydrogenase from watermelon: sequence of cDNA clones and primary structure of the higher-plant precursor protein

The isolation and sequence of a cDNA clone encoding the complete mitochondrial malate dehydrogenase (mMDH) of watermelon cotyledons is presented. Taking advantage of the polymerase chain reaction technology partial cDNA clones from the central part, the 3 part and the 5 part of the mRNA were obtained with oligonucleotides based on directly determined amino acid sequences. Subsequently, two complete cDNA clones for mMDH were synthesized with a sense primer corresponding to the nucleotide sequence of the amino terminal end of pre-mMDH and two antisense primers corresponding to the major alternative adenylation sites found in the mRNA.The amino acid residues for substrate and cofactor binding identified by X-ray crystallography for pig heart cytoplasmic MDH are conserved in the 320 amino acid long mature higher-plant mMDH. A presequence of 27 amino acids is present at the amino terminal end of the precursor protein.     

Studies on the mechanism of photosystem II photoinhibition I. A two-step degradation of D1-protein

The role of D1-protein in photoinhibition was examined. Photoinhibition of spinach thylakoids at 20°C caused considerable degradation of D1-protein and a parallel loss of variable fluorescence, Q_B-independent electron flow and Q_B-dependent electron flow. The breakdown of D1-protein as well as the loss of variable fluorescence and Q_B-independent electron flow were largely prevented when thylakoids were photoinhibited at 0°C. The Q_B-dependent electron flow markedly decreased under the same conditions. This inactivation may represent the primary event in photoinhibition and could be the result of some modification at the Q_B-site of D1-protein. Evidence for this comes from fluorescence relaxation kinetics following photoinhibition at 0°C which indicate a partial inactivation of Q_A ^--reoxidation. These results support the idea of D1-protein breakdown during photoinhibition as a two step process consisting of an initial inactivation at the Q_B-site of the protein followed by its degradation. The latter is accompanied by the loss of PS II-reaction centre function.Abbreviations Asc ascorbate - p-BQ 1, 4-benzoquinone - DAD diaminodurene - DPC diphenylcarbazide - DQH₂ duroquinole - Fecy ferricyanide - MV methylviologen - Q_A primary quinone acceptor of PS II - Q_B secondary quinone acceptor of PS II - SiMo silicomolybdate     

Changes in ribulosebisphosphate carboxylase/oxygenase and ribulose 5-phosphate kinase abundances and photosynthetic capacity during leaf senescence

The abundances of ribulose-1,5-bisphosphate carboxylate/oxygenase (Rubisco) and ribulose-5-phosphate (Ru5P) kinase in field-grown soybean (Glycine max L. Merr.) leaves were quantified by a Western blot technique and related to changes in chlorophyll and photosynthetic capacity during senescence. Even though the leaf content of Rubisco was approximately 80-fold greater than that of Ru5P kinase, the decline in the levels of these two Calvin cycle enzymes occurred in parallel during the senescence of the leaves. Moreover, the decrease in the content of Rubisco was accompanied by parallel decreases of both the large and small subunits of this enzyme but not by an accumulation of altered large or small subunit isoforms. With increasing senescence, decreases in abundances of Rubisco, Ru5P kinase and chlorophyll were closely correlated with the decline in photosynthetic capacity; thus, the specific photosynthetic capacity when expressed per abundance of any of these parameters was rather constant despite an 8-fold decrease in photosynthetic capacity. These results suggest that during senescence of soybean leaves the chloroplast is subject to autolysis by mechanisms causing an approximately 80-fold greater rate of loss of Rubisco than Ru5P kinase.Jointly supported by the United States Department of Agricultural Research Service and the Kentucky Agricultural Experiment Station, Lexington (paper No. 88 3 286).Mention of a commercial product does not constitute endorsement by the United States Department of Agriculture.     

Differential effects of lithium on agonist-stimulated inositol polyphosphate formation in rat cerebral cortex slices: Selective actions on muscarinic cholinergic responses

Recent data indicate that BMY 7378 demonstrates high affinity, selectivity and low intrinsic activity at hippocampal 5-HT_1A receptors, suggesting that BMY 7378 may represent the first selective 5-HT_1A functional antagonist. The present study examined the agonist and antagonist properties of BMY 7378 at spinal cord 5-HT_1A receptors. In electrophysiological studies, iontophoretic administration of either the 5-HT_1A agonist 8-OH-DPAT (43.8 ± 5.4 nA) or BMY 7378 (46.3 ± 5.2 nA) significantly inhibited the firing rate of wide-dynamic-range dorsal horn units indicating that BMY 7378 demonstrates significant intrinsic activity at spinal cord 5-HT_1A receptors. Concomitant BMY 7378 and 8-OH-DPAT administration identified no BMY 7378 ejection current (20–100 nA) which antagonized the 8-OH-DPAT induced inhibition of dorsal horn unit activity. In behavioral studies in the spinal rat, 8-OH-DPAT increased the animals' sensitivity to noxious levels of mechanical stimulation (ED₅₀ = 269 ± 24 nmol/kg) as did BMY 7378 (ED₅₀ = 295 ± 70 nmol/kg) with no statistically significant difference in the maximal response (Y_max) observed. Concomitant BMY 7378 and 8-OH-DPAT administration identified no BMY 7378 dose (10–1100 nmol/kg) which blocked the hyperalgesic effect of 8-OH-DPAT, rather, each drug produced similar effects which were additive. Further, the 5-HT_1A agonist effects of BMY 7378 were blocked by the 5-HT_1A antagonist, spiperone. Therefore, both the electrophysiologic and reflex data indicate that BMY 7378 possesses significant intrinsic activity at spinal cord 5-HT_1A receptors, and like 8-OH-DPAT is a partial agonist at these receptors. Differences in BMY 7378 intrinsic activity at spinal cord as opposed to hippocampal 5-HT_1A receptors are discussed in terms of regional differences in G-proteins coupled to 5-HT_1A receptors in these two CNS regions.     

Isolation of a crustaceann-acetyl-d-glucosamine-1-phosphate transferase and its activation by phospholipids

Summary Then-acetyl-d-glucosamine-1-phosphate: dolichol phosphate transferase fromArtemia has been partially purified and characterized. The enzyme is solubilized from crude microsomes using Triton X-100, and after detergent removal appears to be associated with phospholipids. Using dolichol phosphate and UDP-n-acetyl-d-glucosamine as substrates, the enzyme catalyzes the formation of dolichol-pyrophosphate-n-acetyl-d-glucosamine. the product identity has been verified by TLC and paper chromatography following mild acid hydrolysis. Under the incubation conditions used only one product is made, i.e., Dol-p-p-GlcNAc. The formation of product is linear with increasing amounts of added protein and with time of incubation. The enzyme requires magnesium ions for activity. Activity of the enzyme is stimulated 6-fold by exogenous dolichol phosphate and is also stimulated by added phospholipids, with optimal activity being obtained in the presence of mixtures of phosphatidylcholine and phosphatidylglycerol. Enzymatic activity is not increased upon addition of GDP-mannose or dolichol phosphate mannose. The enzyme is rapidly inactivated by exposure to several detergents, including Triton X-100 and deoxycholate. The activity is inhibited by tunicamycin and by the purified B₂ homologue of this antibiotic. Other antibiotic inhibitors such as diumycin and polyoxin D have little effect on the enzyme. Both the microsomal and solubilized enzyme preparations are inactivated by 70% upon treatment with phospholipase A₂; activity may be restored by addition of phospholipids. Following hydrophobic interaction chromatography on Phenyl Sepharose, gel filtration chromatography on Sepharose CL-4B indicated that the enzyme, purified 81-fold, contained phophatidylcholine and phosphatidyl-ethanolamine.Abbreviations SDS sodium dodecyl sulfate - PMSF phenyl methanesulfonylfluoride - HEPES 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid - GlcNAc N-acetyl-d-glucosamine - Dol-PP-GlcNAc dolichol pyrophosphate N-acetyl-d-glucosamine - Dol-P-man dolichol-phosphate-mannose - Dol-PP- (GlcNAc)₂ dolichol-pyrophosphate-di-N- acetylchitobiose - DMSO dimethylsulfoxide - C:M (2:1) chloroform:methanol (2:1) - C:M:W (10:10:3) chloroform:methanol:water (10:10:3) - GlcNAc-1-P N-acetyl-d-glucosamine-1-phosphate - Dol-P dolichol phosphate - EGTA ethylene glycol bis (b-aminoethyl ether)-NNNN tetraacetic acid     

Small-scale environmental heterogeneity and the analysis of species distributions along gradients

Abstract. The observed distribution of a species along an environmental gradient is strongly affected by environmental variability within a quadrat. Because a quadrat does not represent a point along an environmental gradient, but rather a range of conditions, it is likely to contain species not typically associated with the mean conditions in the quadrat. Systematic relationships exist between a species' true distribution, the observed distribution as a function of mean quadrat environment, and the frequency distribution of the environment within that quadrat. The observed species habitat breadth increases and the observed maximum abundance decreases as within-quadrat environmental heterogeneity increases. If species distributions or beta diversities are to be compared among species or coenoclines, they should be correctedforintra-quadratheterogeneity.Wederive simple corrections for environmental heterogeneity. The distributions of hardwood forest understory species along a soil acidity gradient in the North Carolina piedmont are presented as an example.     

Detection of Myoglobin-Derived Radicals On Reaction of Metmyoglobin With Hydrogen Peroxide and Other Peroxidic Compounds

The reaction of metmyoglobin with equimolar concentrations of hydrogen peroxide has been studied using both electron spin resonance (e.s.r.) and optical spectroscopy. Using the former technique a strong anisotropic e.s.r. signal is observed, in the presence of the spin trap DMPO, which decays relatively rapidly. This previously unobserved signal, which is also observed on reaction of metmyoglobin with a number of other powerful oxidants (peracetic acid, 3-chloroperoxybenzoic acid, monoperoxyphthalic acid, iodosyl benzene, ¹BuOOH and cumene hydroperoxide) is assigned to a slowly-tumbling, metmyoglobin-derived, spin adduct. The parameters of this signal (a_N 1. 45, a_H 0.83 mT) are consistent with the trapped radical having a heteroatom centre; this is believed to be oxygen. The concentration of this species is not affected by compounds such as 2-deoxyribose, mannitol and phenylalanine which are all efficient hydroxyl radical scavengers, demonstrating that the formation of this radical is not due to reaction of “free” HO· generated by breakdown of H₂O₂, by released iron ions. The concentration of this species is however decreased by desferal, ascorbate, Trolox C, salicylate and, to a lesser extent, linoleic acid; with the first three of these compounds further substrate-derived radicals are also observed. Examination of similar reaction systems (though in the absence of DMPO) by optical spectroscopy shows that the myoglobin (IV) species is formed and that this species behaves in a somewhat different manner with these added compounds. These results suggest that the radical trapped in the e.s.r. experiments is a myoglobin-derived species, probably a tyrosine peroxyl radical, arising from oxidative damage to the globin moiety.

The diminution of both the e.s.r. signal of the spin adduct and the optical absorption of the myoglobin (IV) species in the presence of linoleic acid suggests that these myoglobin-derived species can initiate oxidative damage but that this process can be ameliorated by the presence of a number of water-soluble compounds such as ascorbate, Trolox C, desferal and salicylate.     

Identification of fungi for sweet whey permeate utilization and eicosapentaenoic acid production

Summary Eighteen selected organisms of theEumycota division of the fungi kingdom were examined for eicosapentaenoic acid production and utilization of sweet whey permeate. The organisms belong to the subdivisionsMastigomycotina, Zygomycotina, Ascomycotina andDeuteromycotina. Seven organisms were initially identified as lactose utilizers (the predominant sugar in sweet whey permeate_ and eicosapentaenoic acid (EPA) producers. Utilization of lactose was demonstrated and EPA production was confirmed for four organisms, all of the subdivisionMastigomycotina. Growth studies showed thatP. ultimum had the best potential for future work.     

The effect of sulfate reduction on the thermophilic (55°C) methane fermentation process

Summary The continuously operated suspended growth anaerobic contact system was utilized to estimate the effect of sulfate reduction on the thermophilic (55°C) methane fermentation process. Results indicated that reduction in methanogenesis in the presence of sulfate was due to two separate, but related, processes;i.e. competitive and sulfide inhibition. Although prevention of competitive inhibition would be difficult under normal fermenter operation, sulfide inhibition could be minimized by environmental selection of sulfide tolerant microbial populations through biomass recycle and pH control. Stable fermenter operation was achieved at soluble sulfide concentrations as high as 330 mg/l soluble sulfide. Using batch fermenters, a maximum thermophilic sulfate reduction rate of 3.7 mg SO₄ ^2––S/g volatile solids (VS)-day was estimated. The importance of reporting sulfate reduction rates on a biomass basis is demonstrated by a simple population adjustment kinetic model.This research study was conducted at the Department of Agricultural Engineering, Cornell University, Riley Robb Hall, Ithaca, NY 14853, U.S.A.