2014 Volume 88 Issue 9 Pages 451-457
It is commonly known that vitamin D is initially metabolized to 25-hydroxyvitamin D (25(OH)D) in the liver, and then 25(OH)D is metabolized to a functionally active form, 1α,25-dihydroxyvitamin D (1α,25(OH)_2D), in the kidney. CYP2R1 is known to be a physiologically important vitamin D 25-hydroxylase in humans. In this study, we examined production of 25-hydroxyvitamin D_2 (25(OH)D_2) using recombinant yeast cells expressing human CYP2R1. When either vitamin D_3 (VD_3) or vitamin D_2 (VD_2) was added to the cell suspension of the CYP2R1-expressing yeast cells in a buffer containing glucose and 3-hydroxyrpropyl-β-cyclodextrin, the corresponding 25-hydroxylated product was detected. However, the conversion ratio was insufficient, which was probably due to a low efficiency of uptake of the substrate by yeast cells. To overcome this problem, we tried to examine the production of 25(OH)D_2 by a novel method using UV irradiation. When the suspension of the CYP2R1-expressing yeast cells in a buffer containing glucose was irradiated with UVB and then incubated at 37℃, 25(OH)D_2 was produced without VD_2 addition. This 25(OH)D_2 production could be due to the conversion of endogenous ergosterol to VD_2 by UV irradiation and thermal isomerization with the consequent conversion of the resulting VD_2 to 25(OH)D_2 by CYP2R1. Expectedly, the productivity of 25(OH)D_2 with this novel method was higher than that with the method to add VD_2 to the cell suspension.
