gamma-Butyrobetaine hydroxylase. Structural characterization of the Pseudomonas enzyme

gamma-Butyrobetaine hydroxylase is a 2-oxoglutarate-dependent dioxygenase that catalyzes the hydroxylation of gamma-butyrobetaine to carnitine, the last step in the biosynthesis of carnitine from lysine. The primary structure of the enzyme from Pseudomonas sp. AK1 has been determined. Sequence analysis of the intact protein and of peptides from essentially three different digests established the presence of a peptide chain containing 383 residues, and an N-terminal truncated form of 382 residues. The two chains have molecular masses of 43,321 Da and 43,207 Da, respectively, and are identical except for the presence or absence of an N-terminal asparagine residue; the shorter form starts with an alanine residue. In preparations of the dimeric protein, the two chains occur in an approximate ratio of 1:1. There are nine cysteine residues and 13 histidine residues, i.e. amino acids which have been postulated as ligands for iron binding. In spite of functional similarities, there appears to be no clear sequence similarities with any of the other mammalian 2-oxoglutarate-dependent dioxygenases so far characterized.