Figure 4: Results of the kinetic experiments, LC-MS/MS was used to quantify the concentration of products and other metabolites. The experiments were conducted at least in duplicate and error bars represent the standard error. (A) Concentration of 1,25(OH)2D3 produced as a function of initial 25(OH)D3 concentration with the complete reaction mixture (♦) and without the addition of CYP27B1 (■). (B) Concentration of (OH)2D3 isomer produced as a function of initial 25(OH)D3 concentration with the complete reaction mixture (♦) and without the addition of CYP27B1 (■). (C) Concentration of 1,25(OH)2D3 produced over time with the complete reaction mixture (♦) and without the addition of CYP27B1 (■). (D) Final concentration of 25(OH)D3 left in the reaction as a function of concentration of CYP27B1 in the assay.