BLOMQUIST, C.*; LIMA, P.; TARRANT, A.; ATKINSON, M.; ATKINSON, S.; Regions Hospital/University of Minnesota, St. Paul; Regions Hospital, St. Paul; Woods Hole Oceanographic Institute, Woods Hole; University of Hawaii, Honolulu; Alaska SeaLife Center/UAF, Seward: 17&beta-Hydroxysteroid Dehydrogenase (17&beta-HSD) in Scleractinian Corals

Objective: Steroid metabolism studies have yielded evidence of 17&beta-HSD activity in corals. This project was undertaken to clarify whether there are multiple forms of 17&beta-HSD, seasonal variation in activity levels and if zooxanthellae contribute to activity. Methods: Coral fragments (M. capitata, T. coccinea) were collected in summer and winter. Zooxanthellae were cultured from M. capitata. 17&beta-HSD activity in homogenates or sonicates was characterized with regard to steroid substrate and inhibitor specificity, coenzyme specificity, Michaelis constants for estradiol (E₂) and NADP, and sensitivity to inhibition by phytochemicals. Results: Six samples each of M. capitata and T. coccinea (three summer, three winter) were assayed with E₂ and NADP. Specific activity (pmol/mg protein/240 min) varied 8-fold (40-320) between M. capitata samples and 5-fold (40-200) between T. coccinea samples. There was overlap of activity levels between summer and winter samples. NADP/NAD activity ratios varied from 1.6 to 21.6 for M. capitata, 2.3 to 3.8 for T. coccinea and 0.65 to 1.1 for zooxanthellae. Coumestrol was the most inhibitory of the steroids and phytochemicals tested. Discussion: Our data show that corals and zooxanthellae contain 17&beta-HSD activity. Activity levels vary between samples. Whether there is seasonal variation remains to be clarified. Marked differences in NADP/NAD and E₂/testosterone activity ratios between coral samples are suggestive of the presence of more than one 17&beta-HSD isoform. The activity in zooxanthellae appears to differ from that in coral.