Effect of Sulfur Nutrition on the Activity of Acetyl Coenzyme A Carboxylase, Citrate Cleavage Enzyme, and Malic Enzyme in Rat Liver

Author

Joyce Brann Bittle, University of Tennessee, Knoxville

Date of Award

6-1977

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Human Ecology

Major Professor

John T. Smith

Committee Members

Jane R. Savage, Irshad Ahmad, Mary Nelle Traylor

Abstract

The level of dietary inorganic sulfate as well as the nature of the neutral sulfate fed a rat have been shown to affect the activity of certain key enzymes of carbohydrate metabolism. Metabolic alterations have been demonstrated in rats fed diets containing inorganic sulfate at levels above or below the established optimal level of 0.02%. The present investigation was designed to extend these studies to include lipogenesis.

Ninety-two adult male rats were fed diets containing 15% casein and supplemented with CaSO₄, methionine, and cysteine in order to prepare diets with different inorganic sulfate levels and different neutral to inorganic sulfate ratios. These diets were fed for a period of 17 days. At the end of the dietary period the rats were sacrificed by decapitation and their livers removed for enzyme analysis. Acetyl CoA carboxylase activity was measured by a fixation of ¹⁴CO₂ from H¹⁴CO₃, citrate cleavage enzyme activity was measured by coupling the reaction catalyzed by citrate cleavage enzyme with the reduction of oxalacetate with malic dehydrogenase and the following the change of absorbance of NADH to NAD, and malic enzyme was measured by following the change of absorbance of NADP to NADPH.

When diets containing constant levels of total sulfur as sulfate supplemented with inverse amounts of methionine and CaSO₄ were fed, a decrease in the activity of acetyl CoA carboxylase and citrate cleavage enzyme and an increase in malic enzyme activity occurred at inorganic sulfate levels above (0.42%) and below (0.0002%) the optimal of 0.02%. However, when methionine supplementation was held constant acetyl CoA carboxylase activity was increased and citrate cleavage enzyme activity was decreased in the livers of rats fed diets containing inorganic sulfate levels above or below the optimal, 0.02%. Under the same dietary conditions malic enzyme activity was increased at the 0.0002% SO₄⁼ level with no difference occurring at the 0.42% level as compared to the optimal level.

The substitution of cysteine for methionine in the diets previously mentioned. resulted in a decrease in the activities of acetyl CoA carboxylase, citrate cleavage enzyme and malic enzyme thus providing additional evidence that cysteine is not the metabolic equivalent of methionine as a dietary supplement.

When diets containing constant levels of total sulfur as sulfate and supplemented with cysteine were fed, acetyl CoA carboxylase activity was decreased and malic enzyme activity was increased at inorganic sulfate levels above or below optimal. Under the same dietary conditions the activity of citrate cleavage enzyme was found to increase as the level of dietary inorganic sulfate increased. When cysteine supplementation was held constant acetyl CoA carboxylase, citrate cleavage enzyme and malic enzyme activity was decreased in the livers of rats fed diets containing sulfate levels above or below the optimal 0.02%.

The data presented in this investigation show that the level of dietary inorganic sulfate as well as the nature of the neutral sulfur may alter the apparent rate of lipogenesis. These data provide additional evidence of a role for dietary inorganic sulfate as a metabolic regulator.

Recommended Citation

Bittle, Joyce Brann, "Effect of Sulfur Nutrition on the Activity of Acetyl Coenzyme A Carboxylase, Citrate Cleavage Enzyme, and Malic Enzyme in Rat Liver. " PhD diss., University of Tennessee, 1977.
https://trace.tennessee.edu/utk_graddiss/3823