Open AccessKinetics and regulation of 25‐hydroxycholecalciferol 1α‐hydroxylase from cells isolated from human term decidua
Author(s) -
DELVIN Edgard E.,
ARABIAN Alice
Publication year - 1987
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1987.tb10915.x
Subject(s) - calcitriol , endocrinology , kinetics , medicine , enzyme , parathyroid hormone , chemistry , substrate (aquarium) , enzyme kinetics , biology , biochemistry , vitamin d and neurology , calcium , physics , active site , ecology , quantum mechanics
Kinetics and regulation of 25‐hydroxycholecalciferol 1α‐hydroxylase from cells isolated from term human decidua were studied. The production of 1α,25‐dihydroxycholecalciferol (calcitriol) was linear with time for up to 6 h and was directly proportional to the number of cells up to 20x10 6 /dish at a substrate concentration of 100 nM. Under these conditions the apparent K m was 88 nM and the V max 3.0 pmol/10 6 cells. The production of [ 3 H]calcitriol was inhibited by 0.1 nM ( P <0.01) and 1 nM ( P <0.005) unlabeled calcitriol. Unlike the kidney enzyme and for reasons that remain unclear, neither inorganic phosphate salts nor parathyroid hormone had any acute effect on the calcitriol production. Further studies are required to delineate the regulatory mechanism of this enzyme.