Specificity of Lysine:N6-Hydroxylase: A Hypothesis for a Reactive Substrate Intermediate in the Catalytic Mechanism

✍ Scribed by L. Marrone; S. Siemann; M. Beecroft; T. Viswanatha

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 231 KB
• Volume: 24
• Category: Article
• ISSN: 0045-2068
• DOI: 10.1006/bioo.1996.0034

✦ Synopsis

The recombinant cytoplasmic preparation of lysine : N 6 -hydroxlase catalyzes the conversion of L-lysine to its N 6 -hydroxy derivative when supplemented with the cofactors NADPH and FAD. A number of lysine analogs reflecting minor alterations in the inherent structural features of the amino acid as well compounds with relatively high affinity for lysine binding domains in other proteins were examined for their ability to serve as substrates of lysine : N 6hydroxylase. These studies have revealed that the enzyme does not tolerate any change in the structural features of L-lysine, its preferred substrate, with the exception of the replacement of the C Ͳ H 2 -methylene group by sulfur, as in (S)-2-aminoethyl-L-cysteine. L-Norleucine is a potent inhibitor of the enzyme while L-norvaline and L-Ͱ-aminobutyric acid do not exhibit such effect, indicating the importance of a C 4 hydrophobic side chain for effective interaction with the enzyme. Among the N-alkyl amides of hydrophobic amino acids, only L-norleucine methylamide and L-Ͱ-aminobutyric acid ethylamide serve as moderate inhibitors of lysine : N 6hydroxylase. Based on the enzyme's stringent substrate specificity, a mechanism involving the conversion of L-lysine to 2-aminocaprolactam prior to its oxygenation by the 4a-peroxyflavin intermediate in the catalytic cycle is proposed.