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61.
The kinetics of the reaction of Golfingia gouldii hemerythrin with O2 have been studied by stopped flow spectrophotometry. For the second order oxygenation process, k1 = 7.4 X 10(6) M-1 s-1, deltaH1++ = 8.2 kcal-mol-1 and deltaS1++ = +1 e.u. at 25 degrees, pH 8.2, and I = 0.015 M. The rate constant is unchanged when protein concentration is varied from 3 to 25 muM, the ionic strength is increased to 0.07 M, and the pH moved to 6.8. The deoxygenation of oxyhemerythrin is studied with stopped flow by scavenging liberated O2 with S2O4(2-). For the first order dissociation, k-1 = 51 s-1, deltaH-1++ = 20.6 kcal-mol-1 and deltaS-1++ = +19 e.u. at 25 degrees, pH 8.2, and I = 0.015 M. The value of k-1 is independent of [protein] = 50 to 200 muM, [S2O4(2-)] = 5 to 100 mM I = 0.015 to 0.30 M and pH 6.8 to 9.0. Using myoglobin instead of S2O4(2-) as scavenger gives similar results. Combination of activation parameters for the oxygenation and deoxygenation processes gives K1 = 1.5 X 10(5) M-1, deltaH = -12.4 kcal-mol-1, and deltaS = -18 e.u., values in good agreement with independent thermodynamic data. Perchlorate ion (0.05 M) enhances k-1 about 3-fold and hardly effects k1. There is no sign of other than a single reaction in either direction, and octameric hemerythrin apparently behaves kinetically as eight single units. 相似文献
62.
An obligately anaerobic bacterium, Eubacterium lentum, was shown to contain cytochromes a, b, and c and a carbon monoxide-binding pigment. Extracts of cells grown with hemin gave a typical absorption spectrum for cytochrome c with maxima at 424, 525, and 553 nm. Extracts from cells grown in the absence of hemin also had an absorption peak corresponding to cytochrome b (562 nm) in their reduced versus oxidized spectrum. Extraction of hemes and formation of pyridine hemochromes allowed quantitation of protoheme IX and heme c. Large amounts of cytochrome c masked the presence of cytochrome b in cells grown in medium containing hemin. When cells were grown in the presence of 50 mM nitrate, cytochrome A (606 nm) was detected. In anaerobic extracts of cells grown either with or without nitrate, cytochromes b and c were reduced by formate and oxidized by NO3. Cytochrome a appeared to be partially oxidized by NO3 and completely oxidized by air. 相似文献
63.
X-ray diffraction studies of lecithin bilayers. 总被引:15,自引:0,他引:15
Counting the individuals in a population before and after an annual period of environmental stress allows the proportion s of the initial population surviving the period to be computed. A series of such observations over n annual periods gives a sequence s1, s2, …, sn. A statistical model is formulated from axioms describing the survival process, and it is concluded that these observed values may usefully be regarded as realizations of a random variable that arises from the normal generated distribution (n.g.d.). Equations for estimating the n.g.d. parameters ζ and τ2 from observed survival proportions by the method of moments and maximum likelihood are given. The distributions of parameter estimates ζ and τ2 are obtained and discussed in the context of testing hypotheses comparing survival among different populations. Finally, the dependence of the n.g.d. upon parameters ζ and τ2 is examined in terms of altering survival, either by population self-regulation mechanisms or man-induced controls. The intent is to provide insight into the relationship between the n.g.d. and its supporting axioms and, more generally, basic knowledge of population processes. 相似文献
64.
Quercetin 3-O-(6″-O-galloyl)-β-d-glucoside has been identified as a constituent of Tellima grandiflora (Saxifragaceae). In all, twelve gallates were encountered: two isomeric gallates of quercetin 3-O-glucoside and two of quercetin 3-O-galactoside, a similar set involving kaempferol, and a similar set involving myricetin. 相似文献
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The removal of cobalt from cobalt(II) bovine carbonic anhydrase by pyridine-2-carboxylate, pyridine-2,6-dicarboxylate and 5-methyl-1,10-phenanthroline occurs via formation of an intermediate. This is presumed to be a ternary adduct of cobalt(II) enzyme with the ligand. In this, metal-protein bonds are loosened, probably via distortion of the normal geometry, resulting in accelerated breakdown of the adduct to apoprotein, compared with the behavior of the cobalt(II) enzyme alone. With 2-carboxy-1,10-phenanthroline, removal of metal is very rapid but no adduct is observed. Values of stability constants of the adducts and rate constants for their decomposition to apoprotein and their formation from apoprotein and cobalt(II) complex were measured at pH 5.5 and 25°C. Formation and dissociation rate constants for the adduct of cobalt carbonic anhydrase with pyridine-2,6-dicarboxylate could be measured from pH 5 to 7 and 10° to 25°C by stopped flow. Values of thermodynamic parameters for the various reactions agreed well with those estimated from the kinetic data. 相似文献
69.
Judd R. Wilkins 《Applied microbiology》1974,27(1):135-140
A simple method for measuring gas production by microorganisms by using a pressure transducer to sense pressure buildup was developed and tested with members of the coliform group. The test system consisted of a 5.0 lb/in(2) pressure transducer and a pressure equalizer valve attached to the metal cap of a test tube (20 by 150 mm); gas pressure was recorded on a strip-chart recorder. Gas pressure response curves consisted of (i) a lag period with no marked increase in pressure, (ii) a rapid pressure buildup period, and (iii) a leveling-off period. A linear relationship was established between inoculum size and length of the lag period. Cultures shaken at 200 oscillations/min showed a marked increase in rate of gas release over stationary cultures. Cell concentrations at the time of rapid buildup in pressure were 10(8)/ml. Mean maximum pressure recordings, lb/in(2) per 10 ml of broth, were: Enterobacter aerogenes, 3.70; Citrobacter intermedium, 2.70; and Escherichia coli, 2.10. Mean CO(2) concentrations, ppm of headspace gas, for E. coli were: (i) 2,000 at time of inoculation, (ii) 25,000 at time of rapid buildup in pressure, and (iii) 150,000 at maximum pressure. These results indicate the potential application of the pressure transducer method for rapidly detecting coliforms and other gas-producing microorganisms in clinical samples and in sterility testing of foods. 相似文献
70.
Eucalyptin and 8-desmethyleucalyptin have been isolated from the leaf wax coatings of several species of Eucalyptus, from Syncarpia glomulifera, Lophostemon confertus and an Angophora hybrid indicating that C-methylated flavones may be fairly distinctive of the family Myrtaceae. Ursolic acid has been isolated from the leaf waxes of E. youmanii, S. glomulifera, Leptospermum petersonii and Melaleuca quinquenervia, friedelin from Lophostemon confertus and 4,6-dimethoxy-2-hydroxyacetophenone from E. michaeliana. 相似文献