Human Biochemistry, Volume 1 - Murray R. 1993

Protein and Amino Acid Metabolism
Conversion of Amino Acids to Specialized Products
Introduction

Amino Acids serve as the primary nitrogen source for animals and act as precursors to a variety of other nitrogenous compounds. Because most of these compounds are no longer amino acids, the processes by which they are formed proceed via metabolic pathways discussed in other sections of the book. Physiologically important products derived from amino acids include heme, Purines, Pyrimidines, Hormones, and Neurotransmitters, particularly bioactive Peptides. In addition, many Proteins contain amino acids that are modified to perform specific Functions, such as calcium binding or cross-linking; in these cases, the original amino acid residues in the respective proteins act as precursors to the modified amino acids. Finally, there are small peptides or peptide-like molecules synthesized independently of Ribosomes that perform specific cellular functions.