Question

Which of the following enzymes changes the aspartate to oxaloacetate?
A. Malate dehydrogenase
B. Aspartate transaminase
C. Hexokinase
D. All of the above

Answer 1

Aspartate is the ionic form of the amino acid, aspartic acid. It is an alpha amino acid which is used in the synthesis of proteins. It is a non-essential amino acid which means the body can synthesize aspartic acid by itself. It is a metabolite in the urea cycle and also participates in gluconeogenesis.

Complete answer:
Let us look at each of the options given in the questions and see what each enzyme does. The first option is malate dehydrogenase. Malate dehydrogenase is an enzyme that is used to interconvert malate and oxaloacetate. It uses as $NA{D^ + }$ or $NAD{P^ + }$ a cofactor. Malate dehydrogenase converts oxaloacetate to malate for the purpose of getting it out of mitochondria. And then it converts malate back to oxaloacetate.
The next is aspartate transaminase. Aspartate transaminase is an enzyme that is taking part in the gluconeogenesis pathway. The main function of this enzyme is to convert aspartate to oxaloacetate. It also catalyses the conversion of alpha-ketoglutarate to glutamate. This enzyme can also form aspartate from oxaloacetate in the reverse reaction and this is very important in the citric acid cycle.
The next enzyme is hexokinase. Hexokinase is an enzyme that is involved in the glycolysis pathway. It catalyses the conversion of glucose to glucose-6-phosphate with the help of a molecule of ATP. This phosphorylation of glucose is the first step in glucose metabolism.

Hence, the right answer as option B – Aspartate transaminase.

Note:
Aspartate transaminase is also called aspartate aminotransferase (AST). The AST test is used by the doctors to check for liver conditions. The levels of AST are generally higher in the liver, heart, muscles and the abnormally high levels of these can indicate some problem. The levels of AST are high whenever there is an injury to the liver.