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1.
Catalytic and allosteric mechanism of AMP nucleosidase from primary, beta-secondary, and multiple heavy atom kinetic isotope effects 总被引:1,自引:0,他引:1
Adenosine 5'-phosphate was synthesized with specific heavy atom substitutions to permit measurement of V/K kinetic isotope effects for the N-glycohydrolase activity of the allosteric AMP nucleosidase and the acid-catalyzed solvolysis of these compounds. The effects of allosteric activation on the kinetic isotope effects together with the kinetic mechanism of AMP nucleosidase [DeWolf, W. E., Jr., Emig, F. A., & Schramm, V. L. (1986) Biochemistry 25, 4132-4140] indicate that the kinetic isotope effects are fully expressed. Comparison of individual primary and secondary kinetic isotope effects with combined isotope effects and the isotope effect of the reverse reaction indicated that kinetic isotope effects in AMP nucleosidase arise from a single step in the reaction mechanism. Under these conditions, kinetic isotope effects can be used to interpret transition-state structure for AMP nucleosidase. Changes in kinetic isotope effects occurred as a function of allosteric activator, demonstrating that allosteric activation alters transition-state structure for AMP nucleosidase. Kinetic isotope effects, expressed as [V/K(normal isotope]/[V/K(heavy isotope)], were observed with [2'-2H]AMP (1.061 +/- 0.002), [9-15N]AMP (1.030 +/- 0.003), [1'-2H]AMP (1.045 +/- 0.002), and [1'-14C]AMP (1.035 +/- 0.002) when hydrolyzed by AMP nucleosidase in the absence of MgATP. Addition of MgATP altered the [2'-2H]AMP effect (1.043 +/- 0.002) and the [1'-2H]AMP effect (1.030 +/- 0.003) and caused a smaller decrease of the 14C and 15N effects. Multiple heavy atom substitutions into AMP caused an increase in observed isotope effects to 1.084 +/- 0.004 for [1'-2H,1'-14C]AMP and to 1.058 +/- 0.002 for [9-15N,1'-14C]AMP with the enzyme in the absence of ATP.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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3.
A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera 总被引:14,自引:1,他引:13
Levels of mitochondrial DNA (mtDNA) sequence divergence between species
within each of several avian (Anas, Aythya, Dendroica, Melospiza, and
Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were
compared. An analysis of digestion profiles generated by 13-18 restriction
endonucleases indicates little overlap in magnitude of mtDNA divergence for
the avian versus nonavian taxa examined. In 55 interspecific comparisons
among the avian congeners, the fraction of identical fragment lengths (F)
ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these
translate into estimates of nucleotide sequence divergence (p) ranging from
0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F
values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater
than 0.070. The small mtDNA distances among avian congeners are associated
with protein-electrophoretic distances (D values) less than approximately
0.2, while the mtDNA distances among assayed fish and amphibian congeners
are associated with D values usually greater than 0.4. Since the
conservative pattern of protein differentiation previously reported for
many avian versus nonavian taxa now appears to be paralleled by a
conservative pattern of mtDNA divergence, it seems increasingly likely that
many avian species have shared more recent common ancestors than have their
nonavian taxonomic counterparts. However, estimates of avian divergence
times derived from mtDNA- and protein-calibrated clocks cannot readily be
reconciled with some published dates based on limited fossil remains. If
the earlier paleontological interpretations are valid, then protein and
mtDNA evolution must be somewhat decelerated in birds. The empirical and
conceptual issues raised by these findings are highly analogous to those in
the long-standing debate about rates of molecular evolution and times of
separation of ancestral hominids from African apes.
相似文献
4.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
5.
The biochemical state and treatment of 73 children and 44 adults up to the age of 40 with proved congenital hypothyroidism were assessed in a regional study in the north of England. The findings showed that a substantial proportion of the patients were having inappropriate treatment or were not taking their treatment regularly and that in some of these there were clinical effects. 相似文献
6.
Abstract Transport of Mn2+ was repressed in Candida utilis cells grown in continuous culture in high-Mn2+ (100 μM Mn2+ ) medium as compared to cells grown in basic (0.45 μM Mn2+ ) and low-Mn2+ (< 0.05 μM Mn2+ ) media. In contrast, no repression of Cu2+ uptake occurred in high-Cu2+ -grown (25 μM Cu2+ ) cells as compared to cells grown in basic medium (0.54 μM Cu2+ ). Cu2+ -limited cells did not hyperaccumulate Cu2+ and there was not significant difference in initial uptake rates for all 3 Cu2+ conditions. Mn2+ uptake appears to be regulated by a mechanism sensitive to the external Mn2+ concentration, whereas Cu2+ transport is not governed in this way by the external Cu2+ . 相似文献
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9.
Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves 总被引:4,自引:0,他引:4
A puzzling population-genetic phenomenon widely reported in allozyme
surveys of marine bivalves is the occurrence of heterozygote deficits
relative to Hardy-Weinberg expectations. Possible explanations for this
pattern are categorized with respect to whether the effects should be
confined to protein-level assays or are genomically pervasive and expected
to be registered in both protein- and DNA-level assays. Anonymous nuclear
DNA markers from the American oyster were employed to reexamine the
phenomenon. In assays based on the polymerase chain reaction (PCR), two
DNA-level processes were encountered that can lead to artifactual genotypic
scorings: (a) differential amplification of alleles at a target locus and
(b) amplification from multiple paralogous loci. We describe symptoms of
these complications and prescribe methods that should generally help to
ameliorate them. When artifactual scorings at two anonymous DNA loci in the
American oyster were corrected, Hardy-Weinberg deviations registered in
preliminary population assays decreased to nonsignificant values.
Implications of these findings for the heterozygote-deficit phenomenon in
marine bivalves, and for the general development and use of PCR-based
assays, are discussed.
相似文献
10.
S. B. Pinion D. E. Parkin D. R. Abramovich A. Naji D. A. Alexander I. T. Russell H. C. Kitchener 《BMJ (Clinical research ed.)》1994,309(6960):979-983
OBJECTIVE--To evaluate the effectiveness and safety of endometrial laser ablation and transcervical resection of the endometrium compared with hysterectomy in the surgical treatment of women with dysfunctional uterine bleeding. DESIGN--Prospective randomised controlled trial. SETTING--Gynaecology department of a large teaching hospital. SUBJECTS--204 women who would otherwise have been undergoing hysterectomy for menorrhagia were recruited between August 1990 and March 1992 and randomly allocated to hysterectomy (n = 99) or conservative (hysteroscopic) surgery (transcervical resection (n = 52) and laser ablation (n = 53)). MAIN OUTCOME MEASURES--Operative complications, postoperative recovery, relief of menstrual and other symptoms, patient satisfaction with treatment after six and 12 months. RESULTS--Women treated by hysteroscopic surgery had less early morbidity and a significantly shorter recovery period than those treated by hysterectomy (median time to full recovery 2-4 weeks v 2-3 months, P < 0.001). Twelve months later 17 women in the hysteroscopy group had had a hysterectomy, 11 for continuing symptoms; 11 women had had a repeat hysteroscopic procedure; 45 were amenorrhoeic or had only a brown discharge; and 35 had light periods. Dysmenorrhoea and premenstrual symptoms improved in most women in both groups. After 12 months 89% (79/89) in the hysterectomy group and 78% (75/96) in the hysteroscopy group were very satisfied with the effect of surgery (P < 0.05); 95% (85/89) and 90% (86/96) thought that there had been an acceptable improvement in symptoms, and 72% (64/89) and 71% (68/96) would recommend the same operation to others. CONCLUSIONS--Hysteroscopic endometrial ablation was superior to hysterectomy in terms of operative complications and postoperative recovery. Satisfaction after hysterectomy was significantly higher, but between 70% and 90% of the women were satisfied with the outcome of hysteroscopic surgery. Hysteroscopic surgery can be recommended as an alternative to hysterectomy for dysfunctional uterine bleeding. 相似文献