A research scientist is studying biochemical reactions that take place in the liver. He cultures hepatocytes in a growth media enriched with glutamate labeled with nitrogen isotopes. After some time, he finds that the nitrogen isotopes are transferred to oxaloacetate, forming aspartate in the process. Which of the following substances is most likely involved in this reaction?

Question

A research scientist is studying biochemical reactions that take place in the liver.  He cultures hepatocytes in a growth media enriched with glutamate labeled with nitrogen isotopes.  After some time, he finds that the nitrogen isotopes are transferred to oxaloacetate, forming aspartate in the process.  Which of the following substances is most likely involved in this reaction?

Quizplus · Accepted Answer

11ec160b_36ba_b694_9249_0150d7c7e330_MD0001_00 Pyridoxine (vitamin B₆) is necessary for the transamination and decarboxylation of amino acids, for gluconeogenesis, and for other essential biochemical processes. Transamination reactions typically occur between an amino acid and an α-keto acid. The amino group is transferred to the α-keto acid from the amino acid, and the α-keto acid thereby becomes an amino acid. For example, glutamate (amino acid) reacts with oxaloacetate (α-keto acid) to form aspartate (the resulting amino acid) and α-ketoglutarate (the resulting α-keto acid). Transaminases (aminotransferases) are the enzymes that catalyze transamination reactions, and pyridoxal phosphate (active vitamin B₆) serves as an essential cofactor for the transaminase. (Choice A) Biotin (vitamin B₇) is a cofactor for all 4 carboxylase enzymes: pyruvate carboxylase, acetyl-CoA carboxylase, propionyl-CoA carboxylase, and 3-methylcrotonyl-CoA-carboxylase. (Choice B) Folic acid (vitamin B₉) is an essential cofactor in nucleic acid synthesis, and a deficiency of either folate or vitamin B₁₂ results in megaloblastic anemia. (Choice C) Many dehydrogenases use NAD+ and NADP+, which are formed from niacin. Niacin (vitamin B₃, or nicotinic acid) deficiency is known as pellagra and is classically associated with the 4 Ds: dermatitis, dementia, diarrhea, and, if untreated, death. (Choice E) Riboflavin (vitamin B₂) is used in dehydrogenase reactions involving FMN and FAD. (Choice F) Thiamine (vitamin B₁) serves as a coenzyme for a number of important dehydrogenase enzymes, including transketolase, α-ketoglutarate dehydrogenase, and pyruvate dehydrogenase. Educational objective: Transamination reactions typically occur between an amino acid and an α-keto acid. The amino group from the amino acid is transferred to the α-keto acid, and the α-keto acid in turn becomes an amino acid. Pyridoxal phosphate (active vitamin B₆) serves as a cofactor in amino acid transamination and decarboxylation reactions. __________ References: Review: the role of coenzymes in clinical enzymology. (http://www.ncbi.nlm.nih.gov/pubmed/337888) An appreciation of Professor Alexander E. Braunstein. The discovery and scope of enzymatic transamination. (http://www.ncbi.nlm.nih.gov/pubmed/2503044) Aspartate aminotransferase: an old dog teaches new tricks. (http://www.ncbi.nlm.nih.gov/pubmed/24121043)

A Research Scientist Is Studying Biochemical Reactions That Take Place