GAMMA-BUTYROBETAINE HYDROXYLASE STRUCTURAL CHARACTERIZATION OF THE PSEUDOMONAS ENZYME

Gamma-Butyrobetaine hydroxylase is a 2-oxoglutarate-dependent dioxygen ase that catalyzes the hydroxylation of y-butyrobetaine to carnitine, the last step in the biosynthesis of carnitine from lysine. The primar y structure of the enzyme from Pseudomonas sp. AK1 has been determined . Sequence analysis of the intact protein and of peptides from essenti ally three different digests established the presence of a peptide cha in containing 383 residues, and an N-terminal truncated form of 382 re sidues. The two chains have molecular masses of 43 321 Da and 43 207 D a, respectively, and are identical except for the presence or absence of an N-terminal asparagine residue; the shorter form starts with an a lanine residue. In preparations of the dimeric protein, the two chains occur in an approximate ratio of 1 : 1. There are nine cysteine resid ues and 13 histidine residues, i. e. amino acids which have been postu lated as ligands for iron binding. In spite of functional similarities , there appears to be no clear sequence similarities with any of the o ther mammalian 2-oxoglutarate-dependent dioxygenases so far characteri zed.