cDNA sequence and expression of a phosphoenolpyruvate carboxylase gene from soybean

A full-length cDNA encoding a subunit of phosphoenolpyruvate carboxylase (PEPC) was isolated from a developing seed expression library of the C₃ plant Glycine max. The corresponding mRNA is present at similar levels in leaf, stem, root and developing seed. Two potential start codons exist, and the activity of protein initiated from the first such codon could be subject to regulation by protein kinase. Sequence comparison shows a similar upstream start codon in the case of the Ppc2 gene from Mesembryanthemum crystallinum, previously assumed to lack the sequences necessary for phosphorylation. The soybean encoded protein tends to resemble other C₃-type PEPC proteins more closely than those implicated in C₄ or crassulacean acid metabolism.     

Metabolism of naphthalene by the biphenyl-degrading bacterium Pseudomonas paucimobilis Q1

Pseudomonas paucimobilis Q1 originally isolated as biphenyl degrading organism (Furukawa et al. 1983), was shown to grow with naphthalene. After growth with biphenyl or naphthalene the strain synthesized the same enzyme for the ring cleavage of 2,3-dihydroxybiphenyl or 1,2-dihydroxynaphthalene. The enzyme, although characterized as 2,3-dihydroxybiphenyl dioxygenase (Taira et al. 1988), exhibited considerably higher relative activity with 1,2-dihydroxynaphthalene. These results demonstrate that this enzyme can function both in the naphthalene and biphenyl degradative pathway.Abbreviations DHBP dihydroxybiphenyl - DHBPDO 2,3-dihydroxybiphenyl dioxygenase - DHDHNDH 1,2-dihydroxy-1,2-dihydronaphthalene dehydrogenase - DHN 1,2-dihydroxynaphthalene - DHNDO 1,2-dihydroxynaphthalene dioxygenase - HBP cis-2-hydroxybenzalpyruvate - HOPDA 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate - PCB polychlorinated biphenyl - 2NS naphthalene-2-sulfonic acid     

Effect of Ozone on the Activities of Reactive Oxygen Scavenging Enzymes in Rbc of Ozone Exposed Japanese Charr (Salvelinus Leucomaenis)

The effect of ozone exposure on the activities of reactive oxygen scavenging enzymes (SOD†, catalase, GSH-Px) in RBC of Japanese charr (Salvelinus leucomaenis) was examined. Ozone (0, 0.4 and 0.7 ppm as initial concentrations) was exposed to Japanese charr for 30 min, which definitely caused serious membrane damage to RBC of fish. Ozone exposure at 0.4 and 0.7 ppm decreased activities of both catalase and GSH-Px by 80 to 57+ of the control. On the other hand, the activities of SOD remained unaffected even by 0.7 ppm ozone exposure. A hypothesis on the RBC membrane damage and participation of SOD and heme-iron was proposed.     

Histidine utilization by Alcaligenes eutrophus: Regulation of histidase formation under heterotrophic conditions of growth

Histidine supported good growth of Alcaligenes eutrophus strain H 16 as a nitrogen source, but only poor growth as a carbon and energy source. The facultative chemolithoautotrophic bacterium was also able to utilize urocanic acid, the first intermediate of histidine catabolism. The products of histidine degradation were ammonium, formate and glutamate. Three enzymes of the pathway, histidase, urocanase and formiminoglutamate hydrolase, were present in histidine-grown cells. Two types of spontaneous mutants, derived from the wild type, were characterized by an increased growth rate on histidine. One of these types was found to produce histidase constitutively and at a higher activity compared with the parental strain. The second type of mutant had apparently gained an improved histidine uptake system, which is supposed to be growth rate-limiting in the wild type. From the physiological studies the conclusion was drawn that the control of histidine-degrading enzymes is based on induction by urocanate and catabolite repression by carbon sources supporting fast growth, such as succinate or pyruvate. Ammonium was found not to affect catabolite repression, however, we obtained evidence that histidine uptake is subject to a nitrogen control.Abbreviation CTAB hexadecyltrimethylammonium bromide     

Hymenolepis diminuta: Partial characterization of the membrane-bound and solubilized alkaline phosphohydrolase activities of the isolated brush border plasma membrane

The membrane-bound and solubilized (using Triton ×-100 or sodium dodecyl sulfate (SDS)) alkaline phosphohydrolase (APase) activities of the isolated brush border membrane of Hymenolepis diminuta require a divalent cation for maximum activity. Highest rates of substrate (p-nitrophenyl phosphate) hydrolysis are obtained with low concentrations of Mg²⁺ (1 mM), although low concentrations of Mn²⁺, Ca²⁺, or Zn²⁺ will also partially satisfy this requirement; higher concentrations of Mg²⁺ and Mn²⁺, and other divalent cations (Cu²⁺, Fe²⁺, and Pb²⁺), inhibit the membrane-bound APase activity. Solubilization of the membrane-bound enzyme in either Triton or SDS results in an increase in specific activity and K_m, but has little effect on thermal stability of the APase activity. Phosphate, pyrophosphate, adenosine 5′-triphosphate, adenosine 5′-monophosphate, glucose 1-phosphate, glucose 6-phosphate, fructose 6-phosphate, and fructose 1,6-diphosphate inhibit substrate hydrolysis, and the relative affinities of these inhibitors for the APase enzyme are altered only slightly upon solubilization. Graphic analyses of data from inhibitor studies indicate that all eight inhibitors will inhibit membrane-bound and solubilized APase activities 100% at high inhibitonsubstrate ratios. Molybdate, F^?, 2-mercaptoethanol, cysteine, and p-chloromercuribenzoate inhibit membrane-bound APase activity. Inhibitor data indicate that if more than one enzyme is responsible for the APase activity of the brush border membrane of H. diminuta, the enzymes cannot be differentiated on the basis of substrate specificity.     

Mg2+ restores membrane potential in rat liver mitochondria deenergized by Ca2+ and phosphate movements

Cellular ornithine biosynthesis could be expected to play a significant role in putrescine formation and hence in growth. Two enzymes are involved in ornithine biosynthesis: arginase and transamidinase. These enzyme activities were studied in two human melanoma cell lines differing in their K_m of diamine oxidase for putrescine and in their tumorigenicity in nude mice. Arginase activity accounts for the majority of ornithine formed in the highly tumorigenic cell line, while the majority of ornithine is derived from transamidinase action in the poorly tumorigenic cell line, with concomitant formation of methyl guanidine, a potent inhibitor of diamine oxidase.     

Cholesterol-Esterifying Enzymes in Developing Rat Brain

Abstract: A cholesterol-esterifying enzyme which incorporates exogenous fatty acids into cholesterol esters in the presence of ATP and coenzyme A was demonstrated in 15-day-old rat brain. This enzyme was maximally active at pH 7.4 and distinct from the cholesterol-esterifying enzyme reported earlier (Eto and Suzuki, 1971), which has a pH optimum at 5.2 and does not require cofactors. Properties of the two enzymes have been compared. Both the enzymes showed negligible esterification with acetate and were maximally active with oleic acid. The pH 5.2 enzyme esterified desmosterol, lanosterol and cholesterol at about the same rate, while the pH 7.4 enzyme was only 50% as active with lanosterol as it was with cholesterol and desmosterol. Phosphatidyl serine stimulated the pH 5.2 enzyme but not the pH 7.4 enzyme. Phosphatidyl choline and sodium taurocholate showed no effect on either of the enzymes. Both the enzymes were associated with particulate fractions, but the pH 7.4 enzyme was localized more in the microsomes. Purified myelin showed 2.6-fold and 1.5-fold higher specific activities of pH 5.2 and 7.4 enzymes respectively, when compared with homogenate. About 7–10% of total activity of both the enzymes was associated with purified myelin. Brain stem and spinal cord showed higher specific activity of pH 5.2 enzyme than cerebral cortex and cerebellum, while pH 7.4 enzyme specific activity was higher in cerebellum and brain stem than in cerebral cortex and spinal cord. Microsomal pH 7.4 activity showed progressive increase prior to the active period of myelination, reaching a maximum on the 15th day after birth and declined to 20% of the peak activity by 30 days. In contrast, pH 5.2 enzyme reached maximum activity about the 6th day after birth and remained at this level well into adulthood. In 15-day-old rat brain, pH 7.4 enzyme had five to six times higher specific activity than pH 5.2 enzyme, while in adults the activities were equal. The pH 7.4 enzyme showed a threefold higher specific activity than pH 5.2 enzyme in myelin from 15-day-old rats, but in adults the reverse was true.     

Effect of water stress on some oxidative enzymes and senescence in Vigna seedlings

Seedlings of Vigna catjang Endl. were subjected to water stress for 6, S and 10 days by withholding water to investigate the activities of some oxidative enzymes and the pattern of senescence in leaves of 17-day-old seedlings undergoing water stress. Increasing duration of stress produced a proportional increase in the activities of IAA-oxidase, AA-oxidase, peroxidase and glycolate oxidase but decreased catalase activity and the contents of both chlorophyll and protein, hastening senescence. Leaf water potential and relative water content were also lowered with incresing duration of stress. Permeability was increased in leaf tissue undergoing water stress for 8 days. Seed treatment with CaCl₂ (10⁻² and 10⁻¹⁴ M ) for 6 h improved the water status of leaves, decreased tissue permeability, activities of oxidative enzymes, decline of chlorophyll and protein contents and delayed senescence compared to untreated water stressed plants.     

Effect of Oxotremorine on Ornithine Decarboxylase Activity of the Adrenal Gland in Rat

Abstract: In this work we have studied the mechanism for the increase of adrenal ODC (ornithine decarboxylase, EC 4.1.1.17) activity provoked by oxotremorine, a muscarinic agonist. 1. Oxotremorine increased medullary ODC activity maximally at 2 h. Cortical enzyme responded much more slowly. 2. Blockade of peripheral muscarinic receptors with methylatropine partially reduced the response to oxotremorine in the medulla, but not cortex. 3. Hy-pophysectomy abolished the cortical, but not the medullary, responses to oxotremorine. Methylatropine reduced the effect of oxotremorine on medullary ODC in hypophysectomized rats. 4. In unilaterally splanchnicotomized rats oxotremorine caused an increase of ODC activity of the denervated adrenal gland relative to control value; activities in both medulla and cortex were significantly lower than those observed in the innervated gland. Evidence was obtained for a compensatory increase of ODC activity of the adrenal cortex (but not medulla) on the intact side of unilaterally operated rats. 5. Surgical intervention, in the form of a sham operation for transection of the spinal cord, leads to an increase of ODC activity in both parts of the adrenal gland. Transection of the cord attenuates these increases. 6. The additional increase of medullary ODC activity owing to the administration of oxotremorine to sham-operated rats is partially reduced in the adrenal medulla by muscarinic blockade, and completely in the cortex. This effect of methylatropine in regard to cortical ODC activity was not apparent in the other experiments with intact or unilaterally splanchnicotomized (unoperated side) rats. The results with unilaterally splanchnicotomized rats and those with transected spinal cord suggest that oxotremorine-induced modifications of adrenal ODC activity are centrally mediated, above the level of origin of the splanchnic nerves in the spinal cord (T_8–10). Experiments with hypophysectomized rats show that the response of the adrenal cortex to oxotremorine is entirely mediated by the hypophysis.