BIOCHEMISTRY - L. Stryer - 1984

VOLUME 1

PART I. CONFORMATION AND DYNAMICS

CHAPTER 2. BASIC CONCEPTS OF PROTEIN STRUCTURE AND FUNCTION

2.2. Modified amino acids supplement the basic set of twenty amino acids

Several Proteins contain modified Amino Acids that are formed by the modification of standard amino acids after their incorporation into a polypeptide chain. For example, Collagen contains hydroxyproline, a hydroxylated derivative of Proline (Fig. 2.16). As will be shown later (Section 9.7), the additional hydroxyl group stabilizes The Structure of the collagen fiber. The Biological Significance of this amino acid modification becomes evident in scurvy, which results from deficient hydroxylation of collagen. Another modified amino acid is γ-carboxyglutamate. Impaired carboxylation of glutamate in prothrombin, a Blood-clotting protein, can lead to hemorrhaging (Section 8.23). Phosphoserine is the most common modified amino acid found in proteins. The action of several Hormones is mediated by the phosphorylation or dephosphorylation of specific Serine residues in various proteins (Section 16.11).

Class="center">Fig. 2.16. Several modified amino acid residues found in proteins: hydroxyproline, γ-carboxyglutamate, and phosphoserine. The groups added to The amino acid residue after its incorporation into the polypeptide chain are shown in red.

Table 2.1. Abbreviations for amino acids