Angiotensin-converting enzyme-like activity in crab gills and its putative role in degradation of crustacean hyperglycemic hormone
2008
Chung, J Sook | Webster, S.G.
Angiotensin-converting enzyme-like enzyme activity (ACELA) was found in Carcinus maenas using reverse phase high performance liquid chromatography (RP-HPLC) analysis of degradation kinetics of a synthetic substrate (Hippuryl-histidyl-leucine) and a specific inhibitor (captopril). Gills contained the highest ACELA, then brain, muscle, and testis, respectively, while no activity was detected in the following tissues: hepatopancreas, hindgut, hypodermis, heart, and hemolymph. ACELA present in gill membranes exhibited a Km of 0.23 mM and Vmax of 7.6 nmol with synthetic substrate. The enzyme activity was dependent on Cl⁻ concentration and was markedly inhibited by captopril, lisinopril, and EDTA. Addition of Zn²⁺ to membranes previously treated with EDTA restored 89% activity, suggesting that C. maenas ACELA is a Zn²⁺ metalloenzyme. Gill membranes prepared from premolt crabs showed similar levels of ACELA to those of the intermolt animals. Administration of captopril in vivo lengthened the half life of circulating CHH, while in vitro incubation of gill membranes with captopril reduced CHH. These results suggest that C. maenas ACELA present in gills is likely to be involved in degradation of this neuropeptide. Arch. Insect Biochem. Physiol. 2008.
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