Glycolysis

Glycolysis describes the first step in the process by which cells utilize glucose to provide for their energy needs. Glucose uptake by cellular glucose transporters (GLUT), is followed by a sequence of enzymatic reactions that constitute glycolysis (Fig. 2). The initial steps in glycolysis are catalyzed by hexokinase and phosphofructokinase, respectively, each of which utilize a molecule of ATP to provide the necessary energy for completion of their role in glucose metabolism. The next step is driven by glyceraldehyde 3-phosphate dehydrogenase and results in the reduction of 2 molecules of (3-NAD+ to yield 2 molecules of (3-NADH, which either enter mitochondria via the malate aspartate shuttle or are utilized by lactate dehydrogenase. The final steps in the process, driven by phosphoglycerate kinase and pyruvate kinase respectively, produce 2 molecules of ATP each and generate the final product of glycolysis, pyruvate. Thus, glycolysis yields a total of 2 molecules of ATP. Clearly, glycolysis is an intensive process that provides for only limited ATP production per cycle. Significantly, however, vascular smooth muscle exhibits a greater dependence on glycolysis than other cell types. In fact, at least 30% of the ATP requirement of smooth muscle may be supplied by glycolysis during normoxia, and this can account for as much as 90% of glucose utilization (38, 68).

Shuttle System Glycolysis

Figure 2. Glycolysis and oxidative-phosphorylation by mitochondria. GLUT, glucose transporter; MAS, malate aspartate shuttle; PC, pyruvate carrier; AS, ATP synthetase; AT, ATP translocase; I, II, III and IV, each complex of the mitochondrial electron transport chain; e", electron transport from complex I and II to complex III via coenzyme Q/ubiquinone, and from complex III to complex IV via cytochrome c, respectively.

Figure 2. Glycolysis and oxidative-phosphorylation by mitochondria. GLUT, glucose transporter; MAS, malate aspartate shuttle; PC, pyruvate carrier; AS, ATP synthetase; AT, ATP translocase; I, II, III and IV, each complex of the mitochondrial electron transport chain; e", electron transport from complex I and II to complex III via coenzyme Q/ubiquinone, and from complex III to complex IV via cytochrome c, respectively.

An important consideration with respect to 02-sensing is that this high level of glycolysis may lead to the generation of substantial amounts of lactate, which must then be removed from the cell (see below). This is because pyruvate derived from glycolysis has two possible fates. It can enter mitochondria via the pyruvate carrier, where it is dehydrogenated to yield acetyl CoA for the Krebs cycle. Alternatively, pyruvate, when surplus to mitochondrial requirements, may be broken down by lactate dehydrogenase to form lactate.

Was this article helpful?

0 0
Reducing Blood Pressure Naturally

Reducing Blood Pressure Naturally

Do You Suffer From High Blood Pressure? Do You Feel Like This Silent Killer Might Be Stalking You? Have you been diagnosed or pre-hypertension and hypertension? Then JOIN THE CROWD Nearly 1 in 3 adults in the United States suffer from High Blood Pressure and only 1 in 3 adults are actually aware that they have it.

Get My Free Ebook


Post a comment