Oxidative Capacity of Muscles Higher levels of succinate dehydrogenase in a muscle would indicate a. higher glycolytic capacity b. higher ATP-PCr capacity c. higher lipolytic capacity d. higher oxidative capacity
The correct answer and explanation is:
Correct Answer: d. higher oxidative capacity
Explanation (300 words):
Succinate dehydrogenase (SDH) is a key enzyme found in the mitochondria of cells. It plays a critical role in both the citric acid cycle (also called the Krebs cycle) and the electron transport chain, which are essential pathways involved in aerobic respiration. Because of its dual role in these mitochondrial processes, SDH serves as an important marker of oxidative metabolism in muscle tissue.
When a muscle contains high levels of succinate dehydrogenase, it indicates that the muscle has a high mitochondrial density and is therefore well-equipped to generate energy through oxidative phosphorylation. This means the muscle can efficiently use oxygen to produce ATP, the energy currency of the cell, over long periods—especially important in endurance activities.
Muscles with high oxidative capacity are typically Type I (slow-twitch) fibers, which are fatigue-resistant and support long-duration, low-intensity activities such as distance running or cycling. These fibers rely primarily on aerobic pathways (oxidation of carbohydrates and fats) rather than anaerobic mechanisms like glycolysis or the ATP-PCr system.
Let’s briefly contrast the incorrect options:
- a. Higher glycolytic capacity refers to the ability to generate ATP quickly through anaerobic breakdown of glucose. This process involves enzymes like phosphofructokinase (PFK), not succinate dehydrogenase.
- b. Higher ATP-PCr capacity relates to short bursts of energy (under 10 seconds), involving phosphocreatine and the enzyme creatine kinase, again not SDH.
- c. Higher lipolytic capacity refers to the breakdown of fats into free fatty acids, involving lipase enzymes. While fat oxidation occurs in mitochondria, SDH itself is not directly involved in lipolysis.
Therefore, higher SDH activity is a strong indicator of higher oxidative capacity, not glycolytic or anaerobic energy systems.