Mammalian forebrain ketimine reductase identified as mu-crystallin; potential regulation by thyroid hormones.
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Hallen A, Cooper AJ, Jamie JF, Haynes PA, Willows RD
Mammalian forebrain ketimine reductase identified as mu-crystallin; potential regulation by thyroid hormones.
J Neurochem. 2011 Aug;118(3):379-87. doi: 10.1111/j.1471-4159.2011.07220.x. Epub 2011 Mar 15.
- PubMed ID
- 21332720 [ View in PubMed]
- 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 mu-crystallin. The identity was confirmed by heterologously expressing human mu-crystallin in Escherichia coli and subsequent chromatographic purification of the protein. The purified human mu-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. mu-Crystallin is also involved in intracellular T3 storage and transport. This research is the first to demonstrate an enzyme function for mu-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.