MCAT Biochemistry
The Beta Oxidation of Odd-Chain Fatty Acids is related to the VOMIT pathway, which stands for valine, odd-chain fatty acids, methionine, isoleucine, and threonine. These precursors, including odd-chain fatty acids, undergo a series of biochemical reactions to eventually form succinyl CoA. Odd-chain fatty acids, similar to even-chain fats, undergo beta-oxidation, producing 3-carbon propionyl CoA during the last round.
The next step in the VOMIT pathway involves propionyl CoA carboxylase (PCC), which uses ATP and vitamin B7, or biotin, to add a CO2 to propionyl CoA, creating methylmalonyl CoA. Methylmalonyl CoA then undergoes a transformation, with methylmalonyl CoA mutase utilizing vitamin B12, or cobalamin, to form succinyl CoA. Succinyl CoA has various roles – it can enter the TCA cycle to generate ATP, participate in gluconeogenesis to produce glucose, or serve as a precursor for heme synthesis.
Lesson Outline
<ul> <li>VOMIT pathway: Valine, Odd-chain fatty acids, Methionine, Isoleucine, and Threonine</li> <li>Biochemical reactions of VOMIT pathway <ul> <li>Odd-chain fatty acids undergo beta-oxidation to make propionyl CoA</li> <li>Amino acids valine, methionine, isoleucine, and threonine are metabolized to propionyl CoA</li> <li>Propionyl CoA carboxylase (PCC) adds CO2 to propionyl CoA, making methylmalonyl CoA</li> <li>Enzyme methylmalonyl-CoA epimerase changes methylmalonyl CoA from the D-to L-conformation</li> <li>Methylmalonyl CoA mutase converts methylmalonyl CoA to succinyl CoA with help from vitamin B12</li> </ul> </li> <li>Succinyl CoA functions <ul> <li>Entering the TCA cycle to make ATP</li> <li>Gluconeogenesis when blood glucose levels are low</li> <li>Precursor to heme</li> </ul> </li> </ul>
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FAQs
In beta oxidation, both odd and even chain fatty acids are broken down into two-carbon acetyl CoA units. However, odd chain fatty acids generate an additional three-carbon compound, propionyl CoA, in their final step. This compound is then converted into succinyl CoA through the VOMIT pathway and can enter the TCA cycle.
Vitamin B12 (cobalamin) and vitamin B7 (biotin) play essential roles in the VOMIT pathway, which converts propionyl CoA to succinyl CoA during the metabolism of odd chain fatty acids. Vitamin B12 is a cofactor for the enzyme methylmalonyl CoA mutase, which catalyzes the conversion of methylmalonyl CoA to succinyl CoA. Vitamin B7 is a cofactor for propionyl CoA carboxylase, which contributes to the formation of methylmalonyl CoA from propionyl CoA.
During beta oxidation of odd chain fatty acids, the final step produces propionyl CoA, which is then converted into succinyl CoA through the VOMIT pathway. Succinyl CoA can enter the TCA cycle, generating substrates such as oxaloacetate that can be used in gluconeogenesis. This allows odd chain fatty acids to contribute to glucose production, unlike even chain fatty acids which generate only acetyl CoA through beta oxidation. (Acetyl CoA cannot serve as a substrate for gluconeogenesis.)
Propionyl CoA is a three-carbon compound produced during the final step of beta oxidation of odd chain fatty acids. It serves as a metabolic intermediate and is converted to succinyl CoA via the VOMIT pathway. This process involves three enzymes: propionyl CoA carboxylase, methylmalonyl CoA racemase, and methylmalonyl CoA mutase. The conversion of propionyl CoA to succinyl CoA allows it to enter the TCA cycle for further metabolism, and ultimately contributes to gluconeogenesis.
The VOMIT pathway (Valine, Odd-chain fatty acids, Methionine, Isoleucine, Threonine) is the sequence of enzymatic reactions responsible for the conversion of propionyl CoA to succinyl CoA during the metabolism of odd chain fatty acids. It involves three enzymes: propionyl CoA carboxylase, methylmalonyl CoA racemase, and methylmalonyl CoA mutase. The VOMIT pathway is vital for the utilization of odd chain fatty acids as an energy source, as it allows the formation of succinyl CoA, which can enter the TCA cycle and participate in gluconeogenesis. Additionally, the VOMIT pathway is also essential for the catabolism of certain amino acids, such as valine, isoleucine, and threonine.
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