We expressed a guinea pig 11β-hydroxylase cDNA (1) in COS-1 cells. In order to find the optimal expression system we compared three expression plasmids, each driven by a different promoter. Although promoters exhibited different transcriptional activities this did not result in different enzymatic activities. Upon cotransfection with bovine adrenodoxin a 5-fold increase of enzyme activity was achieved. A comparison with the bovine 11β- hydroxylase clearly demonstrated that the guinea pig enzyme was not able to produce significant amounts of 18-hydroxylated and 18-oxidized products from deoxycorticosterone under the experimental conditions used.
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