Glycerol kinase is an enzyme that is important in lipolysis, or the breakdown of proteins. It works by transferring a phosphate group from ATP, which is the main molecule the human body uses for energy, to a glycerol molecule, which makes a compound called glycerol phosphate. Since glycerol kinase catalyzes this phosphate group transfer, it is part of a class of enzymes called phosphotransferase enzymes. An alternative name for this enzyme is glycerokinase.
The glycerol targeted by glycerol kinase usually comes from the breakdown of triglycerides for energy. Glycerol kinase is important in metabolism because it allows glycerol to be used in the glycolysis pathway, the body's main pathway for deriving energy. The glycolysis pathway breaks down glucose, which is a simple sugar and the body's main source of energy. Although glycerol cannot be used directly in the glycolysis pathway, glycerol phosphate can, and is an essential intermediate in the pathway. The action of glycerol kinase helps replenish and maintain this intermediate so extraction of energy can continue smoothly.
Glycerol kinase deficiency (GKD) is caused by the deletion of a particular region on the X chromosome. A deficiency in this important enzyme can lead to a variety of health problems. These problems can include, but are not limited to, abnormally high blood pH and high levels of glycerol in blood and urine. The more obvious common systems are periodic vomiting and fatigue.
Since GKD is an inherited genetic disease it cannot be cured, but it can be controlled and monitored. Treatment of GKD depends upon both the extent of a particular person's symptoms and the amount of genetic material missing from the X chromosome. The erroneous removal of DNA from the X chromosome may impact other genes nearby, so GKD can at times be coupled with other conditions that result from errors in those genes. Sometimes, the condition can be controlled with a low-fat diet, because this would minimize the amount of excess glycerol in the blood. For people with other conditions or particularly severe cases of GKD, infusion of gluticocorticoids, or steroids that help control glucose metabolism, may be necessary.
Bacteria also have a version of glycerol kinase, and a deficiency in the enzyme results in the same pattern as that observed in humans, where the bacteria are unable to use glycerol. The bacterial version of this gene differs from the human version in that it is one long region of DNA, while the human version is broken up into multiple smaller pieces. In bacteria, the gene is called an operon, or single genetic unit, while in humans, the gene is broken into small coding units called muliple exons.