What is a "limiting" amino acid in a protein? a. an essential amino acid present in insufficient quantity for body protein synthesis to take place b. a nonessential amino acid present in high amounts, which inhibits protein synthesis c. an amino acid of the wrong structure to be utilized for protein synthesis efficiently d. an amino acid that has the paradoxical effect of causing catabolism e. an amino acid that limits the absorption of other essential amino acids by competing with them for transport sites within the gi tract