Hopkins Marine Station Student Paper

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Title: Glycolytic enzyme activities in the liver and white muscle of Gillichthys mirabilis under hypoxic stress
Student Author(s): Troll, Joshua
Faculty Advisor(s): Somero, George
Pages: 21
Location: Final Papers Biology 175H
Date: June 1999
Abstract: Changes in the activity of glycolytic enzymes in response to hypoxic stress has been observed in many different species. I examined the enzymatic response of Gillichthys mirabilis (common name: longjawed mudsucker; family Gobiidae) to hypoxia. The critical oxygen tension (Pc) for G. mirabilis, the tension below which the rate of oxygen consumption precipitously drops, was approximately 1.1 mg/L. I subjected 26 fish to hypoxic stress by reducing the [O2] in their aquarium to 0.3 ± 0.1 mg/L below their Pc. Fish were sacrificed at four time points after the onset of hypoxic stress: 0, 8, 24, and 72 hours. I assayed liver and white muscle tissue from each fish for activities of 5 enzymes involved in anaerobic catabolism of glucose: phosphoglucoisomerase, enolase, pyruvate kinase, lactate dehydrogenase and hexokinase (liver only). No significant change in any of these glycolytic enzymes was observed, indicating that the concentrations of these enzymes do not change during 72 hours of hypoxia. I also assayed liver and white muscle for the concentration of fructose-2,6-bisphosphate (FBP), a potent activator of phosphofructokinase, a rate-governing enzyme of the glycolytic pathway. Significant increases in FBP levels were observed between the 0 and 8 hour time points in the liver (p=0.018) and between the 0 and 72 hour time points in white muscle (p=0.017). It is likely that the increase in FBP levels promotes an increase in glycolytic flux to compensate for decreased aerobic ATP production under hypoxic conditions. Thus, modulation of pre-existing glycolytic enzymes, rather than increased concentration of the enzymes, seems to be responsible for elevating glycolytic activity during hypoxia.