Answer- Case study- Amino acid supplements- A 27- year-old, semiprofessional tennis player seeks advice from a hospital-based nutritionist…


A 27- year-old, semiprofessional tennis player seeks advice from a hospital-based nutritionist concerning his diet supplements. His coach had given him amino acid supplements consisting of phenyl alanine and tyrosine. The rationale was that these precursors to several neurotransmitters will “help his brain focus” on his game. In reality, the excess amino acids are used for energy, with a poor and eclectic diet. Phenyl alanine upon metabolism enters TCA cycle as which of the following?

A. Oxaloacetate

B. Fumarate

C. Succinyl co A

D. Citrate

E. α- Keto glutarate

Answer- The right answer is B- Fumarate.

Phenyl alanine is both a glucogenic as well as ketogenic amino acid. Upon metabolism, it produces one molecule of Fumarate and one molecule of Acetoacetate. Fumarate is an intermediate of TCA cycle that can be converted to oxaloacetate .Thus fumarate represents the glucogenic component of Phenyl alanine. The other component, Acetoacetate can be cleaved by thiolase to give two molecules of Acetyl co A. Acetyl co A is a precursor of ketone bodies. Thus acetoacetate represents the Ketogenic component of Phenyl alanine (figure).

Metabolism of tyrosine

Figure- Phenyl alanine is hydroxylated to form Tyrosine and that is further metabolized to fumarate and Acetoacetate.

Amino acid supplements are used by body builders. Apart from that amino acids are precursors of neurotransmitters; hence they are also used as stimulants of brain activities. Phenyl alanine is converted to Tyrosine in the first step of metabolism, which is a precursor of catecholamines. Tryptophan is a precursor of serotonin and melatonin. Glutamic acid is a precursor of GABA (gamma amino butyric acid), itself also Glutamic acid is a neurotransmitter. Glycine is also a neurotransmitter.

It is true that amino acids are precursors to synthesize neurotransmitters, but excess amino acid consumption leads to degradation.

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