Mammalian forebrain ketimine reductase identified as μ-crystallin; Potential regulation by thyroid hormones

André Hallen, Arthur J L Cooper, Joanne F. Jamie, Paul A. Haynes, Robert D. Willows*

*Corresponding author for this work

Research output: Contribution to journalArticle

43 Citations (Scopus)

Abstract

Ketimine reductase (E.C. 1.5.1.25) was purified to apparent homogeneity from lamb forebrain by means of a rapid multi-step chromatography protocol. The purified enzyme was identified by MS/MS (mass spectrometry) as μ-crystallin. The identity was confirmed by heterologously expressing human μ-crystallin in Escherichia coli and subsequent chromatographic purification of the protein. The purified human μ-crystallin was confirmed to have ketimine reductase activity with a maximum specific activity similar to that of native ovine ketimine reductase, and was found to catalyse a sequential reaction. The enzyme substrates are putative neuromodulator/transmitters. The thyroid hormone 3,5,3′-l-triiodothyronine (T3) was found to be a strong reversible competitive inhibitor, and may have a novel role in regulating their concentrations. μ-Crystallin is also involved in intracellular T3 storage and transport. This research is the first to demonstrate an enzyme function for μ-crystallin. This newly demonstrated enzymatic activity identifies a new role for thyroid hormones in regulating mammalian amino acid metabolism, and a possible reciprocal role of enzyme activity regulating bioavailability of intracellular T3.

Original languageEnglish
Pages (from-to)379-387
Number of pages9
JournalJournal of Neurochemistry
Volume118
Issue number3
DOIs
Publication statusPublished - Aug 2011

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