Kynurenine 3-monoxygenase

Kynurenine 3-monoxygenase is present in the outer membrane of rat liver mitochondria, where it catalyzes the oxidation of L-kynurenine to 3-hydroxy-L-kynurenine. This assay follows the disappearance of the substrate, l-[G-3H]kynurenine. 

Kynurenine was separated from L-3-hydroxykynurenine by chromatography on a Waters /uBondapak Qg column (8 mm X 100 mm, 10-/i,m), using a flow rate of 3 mL/min. The mobile phase was 0.02 M sodium acetate (pH 5.5) containing 2% methanol. Radioactivity was quantitated with a flow-through detector, using scintillation fluid at 3 mL/min. 

The reaction mixture contained 0.1 Af Tris acetate (pH 8.0), 10 mAf KC1, 1 m M EDTA, 3 mAf glucose-6-phosphate, 1 U/mL glucose-6-phosphate dehy- 

Rat liver mitochondria were isolated in 0.25 M sucrose by standard procedures. 

The enzyme also known as methionine synthetase catalyzes the conversion of homocysteine to methionine using a folate derivative as the methyl donor. The assay of Garras et al. (1991) is based on quantitation of the o-phthaldehyde derivative of methionine. 

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