Substrate specificity of a recombinant chicken β-carotene 15,15′-monooxygenase that converts β-carotene into retinal

Abstract

The recombinant β-carotene 15,15′-monooxygenase from chicken liver was purified as a single 60 kDa band by His-Trap HP and Resource Q chromatography. It had a molecular mass of 240 kDa by gel filtration indicating the native form to be tetramer. The enzyme converted β-carotene under maximal conditions (pH 8.0 and 37°C) with a k _cat of 1.65 min⁻¹ and a K _m of 26 μM and its conversion yield of β-carotene to retinal was 120% (mol mol⁻¹). The enzyme displayed catalytic efficiency and conversion yield for β-carotene, β-cryptoxanthin, β-apo-8′-carotenal, β-apo-4′-carotenal, α-carotene and γ-carotene in decreasing order but not for zeaxanthin, lutein, β-apo-12′-carotenal and lycopene, suggesting that the presence of one unsubstituted β-ionone ring in a substrate with a molecular weight greater than C₃₀ seems to be essential for enzyme activity.