| Description |
Most of the cholesterol present in an animals is produced by synthesis. On the average, diet provides only 15 percent of the total amount obtained each day. Cholesterol is a product of animal metabolism, the greater portion is produced by liver cells. The source of the carbon atoms for cholesterol synthesis is Acetyl-CoA. The first important step is the formation of mealonic acid from Acetyl-CoA. Isoprenoid units are formed with a resultant loss of carbon dioxide. Six of these units condense with each other to form squalene, which transforms into lanosterol. Lanosterol is then the parent of several other steroids finally yielding cholesterol. The main purpose of this project was to determine as nearly as possible within the time available and under the restrictions of the assay techniques, whether or not any or all of the enzymes responsible for the conversion of mevalonate to isopentenyl pyrophosphate are present on or in mitochondria. It is known that the enzymes under discussion (mevalonate kinase, phospho-mevalonate kinase, pyrophospho-mevalonate decarboxylase) are all present in the cytoplasm of liver cells. Mitochondria have been shown through intensive research to be the principal site of energy production and transduction for eucaryotic cells. Enzymes for the krebs cycle, B-oxidation of fatty acids as well as several others appear to be in the mitochondrial inter-meranous space or inside the matrix confined by the inner membrane. This membrane itself is the site of electron transport form NADH and succinate to oxygen. Thus most of the enzymes which would normally be expected in mitochondria are not directly concerned with sterol brosynthesis. Thus, if these enzymes are found, it would lead to new paths of research concerning possible other fucntions of these organelles. Also, a finding of this type would be in harmony with the modern ideas that mitochondria in eucaryotic cells arose from a symbiotic incorporation of an anaerobic prokaryote. |
