Date of Award
1987
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
Hormonal control of trehalose synthesis in the fat body of the cockroach, Periplaneta americana, is accompanied by a large decrease in the flux of metabolites through the glycolytic pathway. The decrease in glycolytic flux was investigated by measuring time-dependent changes in the concentrations of glycolytic intermediates at various times after treating the fat body with corpus cardiacum (CC) extract. The data indicate that the CC stimulates trehalose synthesis by a mechanism which includes inhibition of the glycolytic pathway.;The concentration of glucose 6-phosphate in fat body which had been treated with CC extract increased by 360 percent after 30 min, whereas that of fructose 6-phosphate and fructose 1,6-bisphosphate increased by only 138 and 150 percent respectively. The concentration of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate were not affected by CC extract. The level of glycerol 3-phosphate in the fat body was increased by 116 percent at 30 minutes. The data provide the first evidence that the decrease in glycolytic activity due to the CC results from the inhibition of aldolase and phosphoglucoisomerase.;CC extract increased the concentration of citrate and isocitrate in the fat body by 240 and 280 percent respectively, while that of {dollar}\alpha{dollar}-ketoglutarate appeared to decrease. The remaining tricarboxylic acid cycle intermediates were unaffected by CC extract.;Evidence from kinetic studies on aldolase showed that citrate (Ki 1.0 {dollar}\pm{dollar} 0.14 mM) and glycerol 3-phosphate (Ki 2.6 {dollar}\pm{dollar} 0.3 mM) are inhibitory and could explain the inhibition of aldolase in CC treated fat body. Glycerol 3-phosphate potentiated the inhibitory effect of citrate on aldolase by increasing the affinity of the enzyme for citrate (Ki 0.45 {dollar}\pm{dollar} 0.08 mM).;The data show also that phosphoglucoisomerase is inhibited by glycerol 3-phosphate (Ki 2.5 {dollar}\pm{dollar} 0.21 mM) in the concentration range that occurs in CC treated tissue. The enzyme is also inhibited by erythrose 4-phosphate (Ki 3.75 {dollar}\pm{dollar} 0.01 {dollar}\mu{dollar}M) and 6-phosphogluconate (Ki 35.0 {dollar}\pm{dollar} 3.0 {dollar}\mu{dollar}M).;CC extract showed no apparent effect on the incorporation of {dollar}\sp{lcub}14{rcub}{dollar}C into trehalose or glycogen from {dollar}\sp{lcub}14{rcub}{dollar}C labelled amino acids. This suggests that gluconeogenesis is not stimulated by CC extract and agrees with the idea that inhibition of glycolysis by CC extract is mediated by an inhibition of aldolase and phosphoglucoisomerase resulting from the accumulation of citrate and glycerol 3-phosphate.
Recommended Citation
Sevala, Veeresh Lingam, "Hormonal Control Of Carbohydrate Metabolism In The American Cockroach, Periplaneta Americana L" (1987). Digitized Theses. 1669.
https://ir.lib.uwo.ca/digitizedtheses/1669