You are analyzing the activity of cells in culture following the introduction of a mutant form of lactate dehydrogenase exhibiting only 20% of normal activity. These cells continue to exhibit a deficit in gluconeogenesis when pyruvate instead of lactate is added as a substrate. Analysis of the NAD+:NADH ratio indicates that it is elevated compared to normal cells. A defect in which of the following enzymes likely explains the observed results in these test cells?

Question

Quizplus · Accepted Answer

In order for gluconeogenesis to occur, the NADH needed by the reversal of the glycolytic glyceraldehyde-3-phosphate dehydrogenase reaction must be supplied by either lactate dehydrogenase or the action of cytosolic malate dehydrogenase. Since there is a deficit in the reduction of NAD₊ to NADH, the additional defective enzyme must be cytosolic malate dehydrogenase.

You Are Analyzing the Activity of Cells in Culture Following