Peptidyl Glycine Hydroxylase Peptide aAmidase

More thanhalf of the peptide hormones undergo postsynthetic modification to form a carboxy terminal amide, which is essential for biological activity. One function of this amidation is to render the peptides more hydrophobic and enhance receptor binding. The amide group is derived from a glycine residue that is to the carboxyl side of the amino acid which will become the amidated terminal of the mature peptide.

The initial reaction is proteolysis of a precursor peptide to leave a carboxy terminal glycine. This is hydroxylated on the a-carbon by peptidyl glycine hydroxylase, a copper-containing enzyme thathas considerable sequence homology with dopamine ^-hydroxylase, and also uses ascorbate as the reduc-tant. A second enzyme, peptidyl hydroxyglycine a-amidating lyase, catalyzes cleavage of the hydroxyglycine to glyoxylate and the amide of the carboxy terminal amino acid, as shown in Figure 13.5. In animals, the two activities occur in a single bifunctional enzyme, although in invertebrates there are separate hydroxylase and lyase proteins (Prigge et al., 2000).

Table 13.1 Vitamin C-Dependent 2-Oxoglutarate-Linked Hydroxylases

Aspartate ß-hydroxylase 7-Butyrobetaine hydroxylase p-Hydroxyphenylpyruvate hydroxylase Procollagen lysine hydroxylase Procollagen proline 3-hydroxylase Procollagen proline 4-hydroxylase Pyrimidine deoxynucleotide dioxygenase Thymidine dioxygenase Thymine dioxygenase Trimethyllysine hydroxylase


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