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1.
In rat parotid or pancreatic islet homogenates incubated at 7 degrees C, hexokinase displayed a greater affinity for but a lower maximal velocity with the alpha-anomer, as distinct from beta-anomer, of D-mannose. The anomeric specificity of mammalian hexokinase was similar in the case of D-mannose and D-glucose, but represented a mirror image of that of yeast hexokinase. 相似文献
2.
A Sener V Leclercq-Meyer J Marchand M H Giroix S P Dufrane W J Malaisse 《The Journal of biological chemistry》1985,260(24):12978-12981
At a low concentration of D-glucose (3.3 mM), the phosphorylation rate of this hexose in rat pancreatic islet homogenates incubated at 8 degrees C is higher with the beta- than with the alpha-anomer, as expected from the anomeric specificity of hexokinase. In the presence of a high concentration of glucose 6-phosphate (3.0 mM), which inhibits hexokinase but not glucokinase, the phosphorylation rates of the two anomers are not significantly different from one another. Nevertheless, in intact islets exposed at 8 degrees C to the same low concentration of D-glucose, the alpha-anomer augments, more than the beta-anomer, the production of lactic acid and net uptake of 45Ca. At the same concentration (3.3 mM), the alpha-anomer is also more potent than the beta-anomer in enhancing insulin release from perfused pancreases stimulated at 37 degrees C by L-leucine or by the combination of Ba2+ and theophylline. It is concluded that the participation of glucokinase is not essential for the anomeric specificity of glycolysis and insulin release in rat pancreatic islets. 相似文献
3.
A Sener M H Giroix V Leclercq-Meyer J Marchand W J Malaisse 《Biochemistry international》1985,11(1):77-84
In pancreatic islet homogenates incubated in the presence of a high glucose concentration (40 mM), the beta-anomer of D-glucose is phosphorylated at a higher rate than the alpha-anomer, whether in the absence or presence of exogenous glucose 6-phosphate. However, in intact islets also exposed to 40 mM D-glucose, the production of 3H2O from D-[5-3H] glucose, the oxidation of D-[U-14C] glucose and the glucose-induced increment in either lactate production or 45Ca net uptake, as well as the release of insulin from isolated perfused pancreases, are not higher with beta- than alpha-D-glucose. It is concluded that the rate of glucose utilization by islet cells is not regulated solely by the activity of hexokinase and/or glucokinase. 相似文献
4.
Impaired uptake of D-glucose by tumoral insulin-producing cells 总被引:1,自引:0,他引:1
At variance with the situation found in normal pancreatic islets, no equilibration of extracellular and intracellular D-glucose concentrations occurs in tumoral insulin-producing cells of the RINm5F line. This unexpected behaviour may account, in part at least, for the abnormal kinetics of glucose utilization in the tumoral cells and their poor secretory response to this hexose. 相似文献
5.
F Malaisse-Lagae M H Giroix A Sener W J Malaisse 《Biological chemistry Hoppe-Seyler》1986,367(5):411-416
The phosphorylation of alpha- and beta-D-glucose by either yeast hexokinase or beef heart hexokinase was measured at both 10 and 30 degrees C. At 30 degrees C, the anomeric specificity of yeast hexokinase represented a mirror image of that of bovine hexokinase, in terms of both maximal velocity and affinity. A decrease in temperature apparently accentuated the anomeric difference in both maximal velocity and affinity of bovine hexokinase. Such a difference consisted in a higher maximal velocity with beta- than alpha-D-glucose, but a greater affinity for the alpha- than beta-anomer. In yeast hexokinase, however, the decrease in temperature suppressed the anomeric difference in maximal velocity and inversed the anomeric difference in affinity. In the case of both enzymes, the fall in temperature decreased more the maximal velocity recorded with alpha-D-glucose than that measured with beta-D-glucose, and severely lowered the Km for alpha-D-glucose, whilst failing to affect significantly the Km for beta-D-glucose. These findings, which allow to reconcile prior apparently conflicting data, reveal that the anomeric behaviour of hexokinase is affected by the ambient temperature. Our data also support the view that hexokinase underwent a phylogenic evolution in terms of its anomeric specificity. 相似文献
6.
The phosphorylation of D-glucose (1.0mM) was measured in homogenates of tumoral islet cells incubated at 7 degrees C in the presence of labelled alpha- and/or beta-D-glucose, with or without exogenous glucose 6-phosphate. The close-to-maximal reaction velocity of hexokinase was higher with beta- than alpha-D-glucose. The latter anomer inhibited beta-D-glucose phosphorylation more than the beta-anomer decreased the phosphorylation of alpha-D-glucose. This behaviour was accounted for by the higher affinity of hexokinase for alpha- than for beta-D-glucose. These direct measurements of the relative contribution of each anomer to the overall rate of glucose phosphorylation in the presence of mixed populations of alpha- and beta-D-glucose validate the concept that the phosphorylation of D-glucose displays anomeric specificity even when the hexose is used at anomeric equilibrium. Glucose 6-phosphate inhibited the phosphorylation of the two anomers more severely when alpha-D-glucose rather than beta-D-glucose was the most abundant anomer. 相似文献
7.
Hardies SC; Martin SL; Voliva CF; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1986,3(2):109-125
8.
A major difference between the divergence patterns within the lines-1 families in mice and voles 总被引:3,自引:0,他引:3
Vanlerberghe F; Bonhomme F; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1993,10(4):719-731
L1 retroposons are represented in mice by subfamilies of interspersed
sequences of varied abundance. Previous analyses have indicated that
subfamilies are generated by duplicative transposition of a small number of
members of the L1 family, the progeny of which then become a major
component of the murine L1 population, and are not due to any active
processes generating homology within preexisting groups of elements in a
particular species. In mice, more than a third of the L1 elements belong to
a clade that became active approximately 5 Mya and whose elements are >
or = 95% identical. We have collected sequence information from 13 L1
elements isolated from two species of voles (Rodentia: Microtinae: Microtus
and Arvicola) and have found that divergence within the vole L1 population
is quite different from that in mice, in that there is no abundant
subfamily of homologous elements. Individual L1 elements from voles are
very divergent from one another and belong to a clade that began a period
of elevated duplicative transposition approximately 13 Mya. Sequence
analyses of portions of these divergent L1 elements (approximately 250 bp
each) gave no evidence for concerted evolution having acted on the vole L1
elements since the split of the two vole lineages approximately 3.5 Mya;
that is, the observed interspecific divergence (6.7%-24.7%) is not larger
than the intraspecific divergence (7.9%-27.2%), and phylogenetic analyses
showed no clustering into Arvicola and Microtus clades.
相似文献
9.
10.
Oylum Erkus Victor CL de Jager Maciej Spus Ingrid J van Alen-Boerrigter Irma MH van Rijswijck Lucie Hazelwood Patrick WM Janssen Sacha AFT van Hijum Michiel Kleerebezem Eddy J Smid 《The ISME journal》2013,7(11):2126-2136
Maintenance of a high degree of biodiversity in homogeneous environments is poorly understood. A complex cheese starter culture with a long history of use was characterized as a model system to study simple microbial communities. Eight distinct genetic lineages were identified, encompassing two species: Lactococcus lactis and Leuconostoc mesenteroides. The genetic lineages were found to be collections of strains with variable plasmid content and phage sensitivities. Kill-the-winner hypothesis explaining the suppression of the fittest strains by density-dependent phage predation was operational at the strain level. This prevents the eradication of entire genetic lineages from the community during propagation regimes (back-slopping), stabilizing the genetic heterogeneity in the starter culture against environmental uncertainty. 相似文献