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Localization and Quantification of Carbonic Anhydrase Activity in the Symbiotic Scyphozoan Cassiopea xamachana

Anne M. Estes^*, Stephen C. Kempf and Raymond P. Henry

Department of Biological Sciences, 101 Rouse Life Science Building, Auburn University, Auburn, Alabama 36849

To whom correspondence should be addressed. E-mail: henryrp{at}auburn.edu

The relationship between density and location of zooxanthellae and levels of carbonic anhydrase (CA) activity was examined in Cassiopea xamachana. In freshly collected symbiotic animals, high densities of zooxanthellae corresponded with high levels of CA activity in host bell and oral arm tissues. Bleaching resulted in a significant loss of zooxanthellae and CA activity. Recolonization resulted in full restoration of zooxanthellar densities but only partial restoration of CA activity. High levels of CA activity were also seen in structures with inherently higher zooxanthellar densities, such as oral arm tissues. Similarly, the oral epidermal layer of bell tissue had significantly higher zooxanthellar densities and levels of CA activity than did aboral bell tissues. Fluorescent labeling, using 5-dimethylaminonapthalene-1-sulfonamide (DNSA) also reflected this tight-knit relationship between the presence and density of zooxanthellae, as DNSA-CA fluorescence intensity was greatest in host oral epithelial cells directly overlying zooxanthellae. However, the presence and density of zooxanthellae did not always correspond with enzyme activity levels. A transect of bell tissue from the margin to the manubrium revealed a gradient of CA activity, with the highest values at the bell margin and the lowest at the manubrium, despite an even distribution of zooxanthellae. Thus, abiotic factors may also influence the distribution of CA and the levels of CA activity.

Abbreviations: AZ, acetazolamide • CA, carbonic anhydrase • C_i, inorganic carbon • DMF, dimethyl formamide • DNSA, 5-dimethylaminonapthalene-1-sulfonamide • E_o, total concentration of free enzyme • EZ, ethoxyzolamide • i, fractional inhibition of enzyme activity at I_o • I_o, zero concentration of inhibitor • K_i, inhibition constant

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