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The human renal 25‐hydroxyvitamin D 3 ‐1α‐hydroxylase: properties studied by isotope‐dilution mass spectrometry
Author(s) -
HAGENFELDT Y.,
BERLIN T.
Publication year - 1992
Publication title -
european journal of clinical investigation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.164
H-Index - 107
eISSN - 1365-2362
pISSN - 0014-2972
DOI - 10.1111/j.1365-2362.1992.tb01455.x
Subject(s) - chemistry , medicine , endocrinology , isotope dilution , kidney , renal cortex , cortex (anatomy) , enzyme assay , enzyme , calcium metabolism , isotope , vitamin d and neurology , specific activity , cytosol , calcium , mass spectrometry , biochemistry , biology , chromatography , physics , quantum mechanics , neuroscience
. The renal 25‐hydroxyvitamin D 3 ‐α‐hy‐droxylase activity has been measured in normal human kidney cortex, using a highly specific assay based on isotope‐dilution mass spectrometry. The cortex was obtained from kidneys removed due to renal tumours. The subcellular distribution of 25‐hydroxyvitamin D 3 ‐1α‐hydroxylase activity was studied. Enzyme activity was only observed in the mitochondrial fraction. Mitochondria from non‐tumourous kidney cortex had a V max of 0.17 ±0.02 pmol min ‐1 mg ‐1 protein and the apparent K m was in the range 14 μmol l ‐1 . There was a tendency to a higher 25‐hydroxyvitamin D 3 ‐1α‐hydroxylase activity in preparations from male kidney (0.21±0.03 pmol min ‐1 mg ‐1 protein) than female (0.12±0.02, P <0.05). A significant inverse correlation between serum phosphate and 25‐hydroxyvitamin D 3 ‐1α‐hydroxylase activity was found. No correlation was observed between enzyme activity and serum levels of 1,25‐dihydroxyvitamin D (total and free index), PTH, total calcium or ionized calcium. The results indicate that there is a sex difference in human 25‐hydroxyvitamin D 3 ‐1α‐hydroxylase activity similar to the one observed in laboratory animals. Furthermore, the data support the hypothesis that serum phosphate is a major regulator of 1,25‐dihy‐droxyvitamin D 3 production in man.