by PhilipJ on 1 June 2008
Lactate dehydrogenase is a safety valve in our pipeline of energy production. Most of the time, our cells break down glucose completely, releasing the carbon atoms as carbon dioxide and the hydrogen atoms as water. This requires a lot of oxygen. If the flow of oxygen is not sufficient, however, the pipeline of energy production gets stopped up at the end of glycolysis. Lactate dehydrogenase is the way that cells solve this problem, at least temporarily.
When we exercise at a normal pace, our cells get plenty of oxygen and sugar is broken down quickly and efficiently. However, during sprints or other over-exertions, there isn’t enough oxygen to go around. In this case, our cells use glycolysis as their primary source of energy, As part of glycolysis, hydrogen from glucose is placed on NAD+ to form NADH. Normally, these hydrogen atoms are then transferred to oxygen to form water. If oxygen isn’t available, the NADH builds up and there isn’t enough NAD+ to continue using glycolysis to make ATP. That’s where lactate dehydrogenase steps in: it combines pyruvate and NADH, producing lactic acid and NAD+. The NAD+ can then be recycled to do another round of glycolysis, quickly producing more energy for the sprint. However, lactic acid builds up and in a matter of a minute or so, you have to stop and let your body recover. As you catch your breath, your body converts the lactic acid back to pyruvate, where it enters your normal flow of aerobic energy production.
More from David Goodsell here.