Block 10 Amino Acid Metabolism

The presence of high levels of glutamate:oxaloacetate transaminase (GOT) and glutamate:pyruvate transaminase (GPT) in A.B.'s serum suggests liver involvement. These enzymes are primarily found in the liver and their elevated levels indicate liver damage or dysfunction. The other organs listed (heart, brain, muscle, lungs) do not typically produce significant amounts of these enzymes, making the liver the most likely organ affected in this case.

The correct answer is metabolism of branched-chain amino acids. Maple syrup urine disease (MSUD) is a genetic disorder that affects the metabolism of branched-chain amino acids (leucine, isoleucine, and valine). In individuals with MSUD, there is a deficiency of an enzyme complex that is responsible for breaking down these amino acids. As a result, these amino acids and their byproducts accumulate in the body, leading to the characteristic odor of maple syrup in the urine. Defects in the metabolism of aromatic or sulfur-containing amino acids, transformation of carbohydrates to amino acids, or one-carbon transfer reactions would not result in this specific symptom.

A deficiency of cystathionine synthase would result in high blood levels of homocysteine (and also methionine). Cystathionine synthase is an enzyme that plays a crucial role in the methionine metabolism pathway. It converts homocysteine to cystathionine, which is further metabolized to produce cysteine. If cystathionine synthase is deficient, homocysteine cannot be converted to cystathionine, leading to its accumulation in the blood. This can increase the risk of atherosclerosis, as high levels of homocysteine have been associated with damage to blood vessels and the development of plaque.

Methionine is both an essential and glucogenic amino acid. Essential amino acids cannot be synthesized by the body and must be obtained through the diet. Glucogenic amino acids can be converted into glucose through various metabolic pathways. Methionine is essential because it is required for the synthesis of proteins and other important molecules in the body. It is also glucogenic because it can be converted into intermediates that can enter the glucose synthesis pathway, providing a source of glucose when needed.

Phenylketonuria is a genetic disorder that affects the metabolism of phenylalanine. In individuals with this disorder, there is a deficiency of the enzyme phenylalanine hydroxylase, which is responsible for converting phenylalanine into tyrosine. As a result, phenylalanine accumulates in the body, leading to the production of phenylpyruvate and phenylketones. These compounds are indicators of the excessive accumulation of phenylalanine, causing the metabolic pathway to have an excess of substrate for the enzymatic reaction. Therefore, the correct answer is "too much substrate accumulation for an enzymatic reaction."

In Maple syrup urine disease (MSUD), there is a deficiency of the branched-chain alpha-ketoacid dehydrogenase enzyme complex, leading to the accumulation of leucine, isoleucine, and valine. This results in the characteristic sweet-smelling urine (maple syrup odor) and neurological symptoms such as encephalopathy. Hypoglycemia and ketonuria are also commonly seen in MSUD. The normal plasma ammonia level helps to differentiate MSUD from other urea cycle disorders, such as ornithine transcarbamoylase deficiency. Long-chain acyl-CoA dehydrogenase deficiency and methylmalonic acidemia would not typically present with elevated levels of leucine, isoleucine, and valine. Vitamin B12 deficiency would not cause the specific pattern of amino acid elevation seen in MSUD.

Coconut protein is considered biologically inferior because it lacks several essential amino acids. Phenylalanine is one of these essential amino acids that is missing in coconut protein. Therefore, to enhance the biological value of transgenic coconuts' protein, it is crucial to ensure that it contains an adequate amount of phenylalanine.

Dihydrobiopterin reductase is an enzyme involved in the synthesis of tetrahydrobiopterin (BH4), which is a cofactor for the enzyme phenylalanine hydroxylase. Phenylalanine hydroxylase converts phenylalanine to tyrosine. Therefore, a deficiency of dihydrobiopterin reductase would lead to decreased levels of BH4, resulting in impaired phenylalanine metabolism and increased blood levels of phenylalanine.

The correct answer is Tyrosinemia I. This is because the patient's symptoms and laboratory findings are consistent with this condition. Elevated levels of GPT, AST, ammonia, and creatinine in the blood are indicative of liver dysfunction, which is a characteristic feature of Tyrosinemia I. Additionally, the presence of a strong cabbage-like smell suggests the accumulation of tyrosine metabolites in the body, which is a characteristic finding in this disorder.

A negative nitrogen balance occurs when the body is breaking down more protein than it is synthesizing. In this case, a political prisoner who went on a hunger strike would most likely experience a negative nitrogen balance because they are not consuming enough protein or calories to meet their body's needs. Without an adequate intake of protein, the body will start breaking down muscle tissue to obtain the necessary amino acids, leading to a negative nitrogen balance.

The correct answer is Arginase. This is because the patient's symptoms, such as vomiting, lethargy, and convulsions, along with laboratory findings of hyperammonemia and elevated levels of glutamine, citrulline, and arginine, suggest a urea cycle disorder. Arginase is the enzyme responsible for the final step of the urea cycle, converting arginine to ornithine and urea. Deficiency in arginase leads to the accumulation of arginine and subsequent elevation of citrulline and glutamine, resulting in hyperammonemia.

The statement "Patients in the left of the diagram metabolize the drug only very slowly" is false. This is because the figure shows that patients in the left of the diagram metabolize the drug at a faster rate compared to patients on the right.