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11.
Evolution of HCN from both rice ( Oryza sativa ) and cocklebur ( Xanthium pennsylvanicum ) seeds increased during a pre-germination period and preceded the evolution of (C2 H4 ). These two species were adopted as the representatives of starchy and fatty seeds, respectively. Ethylene promotes seed germination of many species. However, HCN evolution declined abruptly when the radicles emerged and before the peak in C2 H4 evolution. More-over, both rice and soybean ( Glycine max ) seeds showed some activity of β-cyanoalanine synthase (CAS, EC 4.4.1.9) even in the unimbibed dry state. The activities of CAS in the lower seed of cocklebur and in soybean seeds increased rapidly after emergence of the radicle. However, the CAS of rice seeds, with high activity in the dry state, exhibited a bimodal change, gradually decreasing until radicle emergence had occurred, but then increaing. It is thus likly that HCN evolution during initial imbibition may be derived from cyanogenic reserves and controlled by both pre-existing and subsequently-developing CAS. The exogenous application of C2 H4 stimulated the activities of CAS in both rice and upper cocklebur seeds and reduced their cyanogen contents. Therefore, the decline of HCN evolution after germination seems to be due to the increased activities of CAS by endogenously produced C2 H4 . 相似文献
12.
Thomas Pazdernik Robert Cross Stanley Nelson Yumi Kamijo Fred Samson 《Neurochemical research》1994,19(11):1393-1400
A poorly understood marked decrease (circa 50% of control) in local cerebral glucose utilization is caused by sublethal doses of NaCN. The decrease is global, occurring in essentially all brain regions and is entirely reversible within hours, leaving no obvious pathology. This event is not unique to NaCN in so far as a strikingly similar pattern of decreased glucose utilization occus with some other toxins. Nor can it be attributed to a direct action of NaCN since local application by microdialysis to the striatum produces a global depression. These results imply that some widely distributed system or substance is involved. We speculate the existence of a system possibly related to the reticular activating system that senses a fall in energy production and acts globally to make cells quiescent and thus would give some protection from excitotoxic driven damage.Special issue dedicated to Dr. Sidney Ochs. 相似文献
13.
Kan Shida Kotaro Takamizawa Masato Nagaoka Takao Tsuji Toshiaki Osawa 《Microbiology and immunology》1994,38(4):273-279
The binding of Escherichia coli heat-labile enterotoxin (LT) type I to glycosylated proteins with lactose (Galβ1-4Glc) by amino carbonyl reaction was studied by the Western blot assay and by the microtiter well binding assay. LT bound to a lactose-α-lactalbumin amino carbonyl product (Lac-LA), whereas cholera toxin did not. The binding ability of Lac-LA was abolished by β-galactosidase treatment, indicating that the terminal galactose is essential for the binding of LT. The binding of LT to Lac-LA was inhibited by galactose and lactose, and most effectively inhibited by lactulose (Galβ1-4Fru), which is a structural analog of the Amadori rearrangement product of the amino carbonyl reaction between lactose and an ε-amino group of a lysine residue (lactuloselysine). The results suggest that LT recognizes the portion of lactuloselysine in Lac-LA. LT also bound to a melibiose (Galα1-6Glc)-α-lactalbumin amino carbonyl product (Mel-LA), but the binding ability of Mel-LA was weaker than that of Lac-LA, suggesting that the β1-4 linked terminal galactose is dispensable but preferable for the binding. Furthermore, LT bound to the amino carbonyl products of lactose with β-lactoglobulin, caseins, bovine serum albumin, and ovalbumin. These results indicate that LT binds to the amino carbonyl products between proteins and sugars containing the terminal galactose, such as lactose. 相似文献
14.
Membrane potential of Thermoplasma acidophila. 总被引:5,自引:0,他引:5
15.
Nicotinamide nucleotide transhydrogenase from beef heart mitochondria was purified to homogeneity and characterized. The enzyme is devoid of other respiratory chain activities as well as flavin. Reduction of NAD+ by NADPH catalyzed by reconstituted transhydrogenase generates an uncoupler-sensitive uptake of lipophilic anions, whereas the rate of reduction of NAD+ by NADPH is enhanced about 13 fold by uncouplers. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate reveales that the protein consists of a single polypeptide of a molecular weight of 97,000. 相似文献
16.
The interaction of acrylonitrile (VCN) with rat blood has been investigated at the molecular level in an attempt to understand the possible mechanism of its toxicity. The results obtained were compared to those with potassium cyanide (KCN), a compound known to liberate cyanide (CN?) in biologic conditions. The radioactivity derived from K14CN was eliminated faster than that from [1-14C]VCN. Up to a maximum of 94% of 14C from VCN in erythrocytes was detected covalently bound to cytoplasmic and membrane proteins, whereas 90% of the radioactivity from KCN in erythrocytes was found in the heme fraction of hemoglobin. Determination of specific activity showed that binding occurred more in vivo than in vitro which indicated that the VCN molecule was bioactivated inside erythrocytes. These results indicate that KCN interacts mainly through CN? liberation and binding to heme, whereas VCN, which binds to cytoplasmic and membrane proteins, may cause damage to red cells by mechanisms other than release of CN?. 相似文献
17.
The role of oxidoreductases in reduction of carbonyl compounds was investigated by application of zymogram techniques. Eight bands were observed using ethanol with nicotinamide adenine dinucleotide (NAD) as coenzyme. Bands observed with lactic acid and (R)-(-)-phenyl-1,2-ethanediol with nicotinamide adenine dinucleotide phosphate (NADP) had similar R(m) values. 2-Hydroxyvalerate and malate manifested bands having similar R(m) values and were active with both NAD and NADP. Based on their structural similarity and identical R(m) values, oxidation of 1,4-cyclooctanediol (band #2) and cis-1,5-cyclooctanediol may be due to a common enzyme. The PAGE-zymogram technique may be used on a preparative scale to facilitate purification and full characterization on the observed stained bands. 相似文献
18.
Media of de Greef & Jacobs (1979) were autoclaved either with all the nutrient components in a single vessel (medium 1) or with the following components in separate vessels: FeNa–EDTA+CaCl2 (medium 2), FeNa–EDTA+NaH2PO4 (medium 3) or sucrose (medium 4). Medium 5 was prepared by autoclaving FeNa–EDTA+NaH2PO4 and sucrose in two separate vessels. It was found that the dry mass yield of cell suspensions ofBeta vulgaris was lowest in medium 1, followed by media 2 and 3. There was no significant difference among media 3, 4, and 5.The plot of dry mass yield of the cell suspensions against the rates of cyanide-initiated oxygen consumption which indicate the extent of carbohydrate hydrolysis of the media during autoclaving, indicated the presence of a threshold rate of about 17–20 nmol ml–1 min–1. Dry mass yield of the suspensions decreased rapidly when the rate exceeded this value.For media with glucose as the source of carbohydrate, the rate of cyanide-initiated oxygen consumption exceeded the threshold value by a factor of 1.5 to 2, depending on the volume of the media autoclaved.Abbreviations FeNa-EDTA
ferric monosodium ethylenediamine-tetraacetic acid 相似文献
19.
Hajime Tokuda Tsutomu Unemoto 《Biochemical and biophysical research communications》1981,102(1):265-271
The membrane potential generated at pH 8.5 by K+-depleted and Na+-loaded is not collapsed by proton conductors which, instead, induce the accumulation of protons in equilibrium with the membrane potential. The generation of such a membrane potential and the accumulation of protons are specific to Na+-loaded cells at alkaline pH and are dependent on respiration. Extrusion of Na+ at pH 8.5 occurs in the presence of proton conductors unless respiration is inhibited while it is abolished by proton conductors at acidic pH. The uptake of α-aminoisobutyric acid, which is driven by the Na+-electrochemical gradient, is observed even in the presence of proton conductors at pH 8.5 but not at acidic pH. We conclude that a respiration-dependent primary electrogenic Na+ extrusion system is functioning at alkaline pH to generate the proton conductor-insensitive membrane potential and Na+ chemical gradient. 相似文献
20.
Relationships among several of the ion movements associated with the acrosome reaction of S. purpuratus were investigated. Egg jelly initiates 45Ca2+ and 22Na+ uptake, and K+ and H+ efflux. H+ efflux and 22Na+ uptake occur with approximately equivalent stoichiometries as rapidly as the appearance of acrosomal rods, perhaps reflecting a linked process. Most K+ loss, as measured either by 42K+ efflux or K+-ion-selective electrodes, occurs after the acrosome reaction is complete. Since an elevation of seawater K+ (from 10 to 15 mM) or the addition of 0.5 mM tetraethylammonium (TEA), an inhibitor of K+ channels, inhibits the acrosome reaction half-maximally, K+ movements or alterations of K+-dependent membrane potentials may regulate the triggering by jelly. Most, but not all, of the 45Ca2+ influx is inhibited with a mixture of 10 μM FCCP, 1 mM CN?, and 2 μg/ml oligomycin, suggesting that the mitochondria store most of the Ca2+. The extracellular Na+ concentration affects Ca2+ fluxes: sperm placed into 5 mM Na+ seawater have enhanced 45Ca2+ uptake, but do not undergo the acrosome reaction, unless 30 mM Na+ is also added. Low Na+ concentrations lead to spontaneous triggering, by allowing for both Ca2+ influx and Na+-dependent H+ efflux. At least one early Ca2+ requirement precedes the Na+ and H+ movements, as inferred from attempts at reversing the inhibitors of jelly induction of the acrosome reaction. When sperm are incubated with jelly in the absence of Ca2+, then washed and incubated with jelly in the presence of Ca2+, the acrosome reaction is triggered only upon the second incubation. However, when sperm are mixed with jelly in the presence of the other inhibitors (verapamil, TEA, 5 mM Na+ seawater, low pH, or elevated K+), they are altered so that even upon subsequent washing, jelly-mediated triggering is no longer possible. This suggests the existence of an intermediate state in the reaction pathway, that follows an event for which Ca2+ is required, but that precedes the Na+ and H+ movements, which are inhibited by all inhibitors of the acrosome reaction. These data are used to develop a partial sequence of ionic changes associated with the triggering mechanism. 相似文献