ISSN:
1432-1793
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Biologie
Notizen:
Abstract A particularly strong reduction of metabolic activity is a precondition for long-term survival ofHalicryptus spinulosus von Siebold under anoxic habitat conditions because of its relatively low fuel reserves (mainly glycogen). The present study analyses the mechanism of this metabolic slow-down. For this purpose the effects of environmental anoxia and exposure to hydrogen sulfide on the activity and selected kinetic properties of glycolytic enzymes [glycogen phosphorylase (GP), pyruvate kinase (PK)] and the concentrations of fructose-2,6-bisphosphate in the body wall ofH. spinulosus were analysed. Anoxia and hydrogen sulfide exposure stimulated modifications of the properties of the enzymes, in both cases due to probable covalent modification of the enzyme proteins. Under both conditions phosphorylase activity was depressed by about 1/3, the result of changes in the percentage of enzyme in the activea-form as well as the total amount of enzyme activity expressed (a +b). Effects of anoxia on the properties of pyruvate kinase included reducedV max , decreasedS 0.5 for phospho-enolpyruvate, changes inK a for fructose-1,6-bisphosphate (an initial decrease was followed by a later increase). TheI 50 forL-alanine of PK was extremely reduced under anoxia and showed an even greater sensitivity to the presence of hydrogen sulfide. Anoxia stimulated a slight reduction in the content of fructose-2,6-bisphosphate, whereas exposure to hydrogen sulfide caused a dramatic decrease of this allosteric activator of phos-phofructokinase. The study gives evidence that mechanisms of glycolytic rate depression are conserved within a wide variety of vertebrate and invertebrate phyla. With two exceptions (fructose-2,6-bisphosphate levels and alanine inhibition of PK) the responses to hydrogen sulfide were the same as those to anoxia, suggesting that at a metabolic level, the consequences of each stress on energy metabolism are similar.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF01314809
