In amino acid catabolism, the first reaction for many amino acids is a (n):

A. decarboxylation requiring thiamine pyrophosphate (TPP).

B. hydroxylation requiring NADPH and O₂.

C. oxidative deamination requiring NAD⁺.

D. reduction requiring pyridoxal phosphate (PLP).

E. transamination requiring pyridoxal phosphate (PLP).

C. oxidative deamination requiring NAD⁺.

Explanation:

Oxidative deamination is the first step in breaking down the amino acids in order to be converted into sugars. This process begins by removal of amino group of the amino acids. The amino group then becomes ammonium as it is lost and subsequently, undergoes the urea cycle to become urea in the liver. From there, It is released into the blood stream, where it is transferred to the kidneys, which will secrete the urea as urine.

The remaining portion of the amino acid becomes oxidized, forming an alpha-keto acid. The alpha-keto acid thus proceed into the Citric acid cycle, in order to produce energy.

The alpha-keto acid can also enter glycolysis, where it will be eventually converted into pyruvate. The pyruvate is then converted into acetyl-CoA so that it can enter the Citric acid cycle cycle and convert the original pyruvate molecules into ATP, or usable energy for the organism.