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1.
Hexaheme nitrite reductases purified to homogeneity from Escherichia coli K-12 and Wolinella succinogenes were studied by low-temperature EPR spectroscopy. In their isolated states, the two enzymes revealed nearly identical EPR spectra when measured at 12 K. Both high-spin and low-spin ferric heme EPR resonances with g values of 9.7, 3.7, 2.9, 2.3 and 1.5 were observed. These signals disappeared upon reduction by dithionite. Reaction of reduced enzyme with nitrite resulted in the formation of ferrous heme-NO complexes with distinct EPR spectral characteristics. The heme-NO complexes formed with the two enzymes differed, however, in g values and line-shapes. When reacted with hydroxylamine, reduced enzymes also showed the formation of ferrous heme-NO complexes. These results suggested the involvement of an enzyme-bound NO intermediate during the six-electron reduction of nitrite to ammonia catalyzed by these two hexaheme nitrite reductases. Heme proteins that can either expose bound NO to reduction or release it are significant components of both assimilatory and dissimilatory metabolisms of nitrate. The different ferrous heme-NO complexes detected for the two enzymes indicated, nevertheless, their subtle variation in heme reactivity during the reduction reaction. 相似文献
2.
3.
M T Thébault J P Raffin J Y Le Gall 《Biochemical and biophysical research communications》1987,145(1):453-459
31P NMR has been used to observe the in vivo phosphometabolite concentrations in the tail musculature from the prawn Palaemon elegans, at rest and after escape swimming and subsequent recovery. Muscular fatigue corresponds to a 60% breakdown of phosphoarginine, and a 45% increase of sugar phosphates. The pHi fell from 7.10 to 6.86. During recovery, the sugar phosphates and arginine phosphate are replenished after 20 minutes. The ATP concentration did not change throughout the experiment. The pHi was restored within 20 minutes. 相似文献
4.
5.
Effects of acetylene on hydrogenases from the sulfate reducing and methanogenic bacteria 总被引:1,自引:0,他引:1
S H He S B Woo D V DerVartanian J Le Gall H D Peck 《Biochemical and biophysical research communications》1989,161(1):127-133
The effect of acetylene on the activity of the three types of hydrogenase from the anaerobic sulfate reducing bacteria has been investigated. The (Fe) hydrogenase is resistant to inhibition by acetylene while the nickel-containing hydrogenases are inhibited by acetylene with the (NiFe) hydrogenase being 10-50 fold more sensitive than the (NiFeSe) hydrogenase. In addition the Ni(III) EPR signal (g approximately 2.3) of the "as isolated" (NiFe) hydrogenase was significantly decreased in intensity upon exposure to acetylene. 相似文献
6.
Protoplasts were isolated from female gametophytes of Chondrus crispus (Stackh.) using commercial cellulase and various carrageenases prepared from marine bacteria. Depending on the nature of the donor tissue (apices or whole thallus, wild or cultivated strains), yields ranged from 1.0–8.5×108 protoplasts per gram of fresh tissue. Preincubating the tissue with a potassium chelator, Kryptofix 222, enhanced protoplast yields by 30–50 %. Based on staining with fluorescein diacetate most protoplasts were viable. A few protoplasts regenerated a cell wall and divided. 相似文献
7.
Age and size at sexual maturity were significantly greater for male mosquitofish, Gambusia affinis Baird and Girard, reared in sib-groups than for their sibs reared individually. Age at sexual maturity averaged 43.3 and 62.1 days for individually- and group-reared males, respectively, a 43% difference; final length and weight at maturity were 7.7 and 34.2% greater, respectively, for group-reared males than for their individually-reared sibs. The results were consistent among 30 families that represented the progeny of 30 wild-caught females. The observed differences may be attributable to behavioural interactions affecting the neuroendocrine control of the maturation process, as suggested by previous studies of Xiphophorus . 相似文献
8.
The nucleolus organizer locus of Xenopus laevis lampbrush chromosomes was identified by in situ hybridization of a 3H-labelled probe complementary to 18S + 28S rDNA. The nucleolus organizer is an axial granule on chromosome III that lies four-fifths the way down this chromosome reading from its larger (left) telomere, just within an exploded region that extends to its right end, where the lateral loops are exceptionally long. By in situ hybridization of 3H-labelled oocyte and somatic 5S spacer cRNA probes to similarly RNase-treated and denatured lampbrush chromosomes, the multiple sites of oocyte and somatic 5S gene families were identified. Oocyte 5S genes lie at the larger telomeres of the 15 chromosomes that possess these structures; that is, all but chromosomes X, XVII and XVIII. There are a further four sites, all peripheral, and in three of these, on chromosomes VII, X and XI, the sequences lie on lateral loops that are resolvable with the light microscope. By contrast all of the somatic 5S gene clusters occupy peripheral sites. There are two sites on chromosome III, one of which may be shared with oocyte 5S sequences; one on chromosome VII, which is very likely shared with oocyte 5S sequences; one terminal site on chromosome X; one site on chromosome XI that lies on a single pair of long loops which are inserted in a conspicuous and recognizable axial granule, loops which certainly carry oocyte 5S sequences too; two nearly terminal sites alongside the larger telomeres on chromosomes XII and XIV; and single interstitial sites on all three of the sphere-bearing chromosomes, VIII, IX and XVI. We suggest that 5S sequences on resolvable loops are transcribed by readthrough from upstream promoters, probably by polymerase II. 相似文献
9.
Maintenance of the cellobiose utilization genes of Escherichia coli in a cryptic state 总被引:6,自引:1,他引:5
The genes for cellobiose utilization are normally cryptic in Escherichia
coli. The cellobiose system was used as a model to understand the process
by which silent genes are maintained in microbial populations. Previously
reported was (1) the isolation of a mutant strain that expresses the
cellobiose-utilization (Cel) genes and (2) that expression of those genes
allows utilization of three beta- glucoside sugars: cellobiose, arbutin,
and salicin. The Cel gene cluster has now been cloned from that mutant
strain. In the course of locating the Cel genes within the cloned DNA
segment, it was discovered that inactivation of the Cel-encoded hydrolase
rendered the host strain sensitive to all three beta-glucosides as potent
inhibitors. This sensitivity arises from the accumulation of the
phosphorylated beta- glucosides. Because even the fully active genes
conferred some degree of beta-glucoside sensitivity, the effects of
cellobiose on a series of five Cel+ mutants of independent origin were
investigated. Although each of those strains utilizes cellobiose as a sole
carbon and energy source, cellobiose also acts as a potent inhibitor that
reduces the growth rate on glycerol 2.5-16.5-fold. On the other hand,
wild-type strains that cannot utilize cellobiose are not inhibited. The
observation that the same compound can serve either as a nutrient or as an
inhibitor suggests that, under most conditions in which cellobiose will be
present together with other resources, there is a strong selective
advantage to having the cryptic (Cel0) allele. In those environments in
which cellobiose is the sole, or the best, resource, mutants that express
the genes (Cel+) will have a strong selective advantage. It is suggested
that temporal alternation between these two conditions is a major factor in
the maintenance of these genes in E. coli populations. This alternation of
environments and fitnesses was predicted by the model for cryptic-gene
maintenance that was previously published.
相似文献
10.
Through the application of a specific oxidase stain to results of starch gel electrophoresis of human serum, three different electrophoretic forms of ceruloplasmin—denoted CpA (fast), CpB (intermediate), and CpC (slow)—have been defined. The electrophoretic differences are small and were first recognized through a rare variant individual who had only the fast and slow forms. Five phenotypes displaying different combinations of the three electrophoretic forms have been defined in American Negroes; these are called CpA, CpAB, CpB, CpAC, and CpBC. Twin, family, and population studies have yielded evidence indicating that the A and B electrophoretic forms are controlled by a pair of autosomal codominant alleles, designated Cp
A
and Cp
B
, and suggesting that the C form may be determined by a third allele, Cp
C
, at the same locus. The variants constitute a genetic polymorphism in American Negroes, but occur only rarely in Caucasians.Supported by U.S. Atomic Energy Commission Contract AT(11-1)-1552, by U.S. Public Health Service Research Grants AM 09381 and HD 02083, and by U.S. Public Health Service Career Development Awards 6-K3-HE-24, 980 (DCS) and 1-K3-A-7959 (GJB). 相似文献