Invertebrate Carbonic Anhydrase: A Central Respiratory and Metabolic Enzyme

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The enzyme, carbonic anhydrase (CA), which catalyses the reversable hydration of CO2 to form bicarbonate ions and hydrogen ions, can potentially play an important role in a number of varied physiological and biochemical processes which involve the molecular and ionic species CO2 : CO2 transport and excretion, CO2 fixation for post-exercise gluconeogenesis, and HCO3- incorporation into carbamoyl phosphate for urea synthesis. Putative multiple function of CA have been studied only sketchily in mammalian/vertebrate systems and not at all among the invertebrates. The purpose of this proposed research is to investigate the role of branchial membrane-associated CA in CO2 excretion in crustaceans under conditions of respiratory stress (e.g., exercise and the transition from water-to air-breathing). Mitochondrial CA will also be investigated with respect to its potential role in supplying HCO3- to the metabolic pathways responsible for gluconeogenesis and urea synthesis. A combination of biochemical, physiological and pharmacological techniques will be used to study CA distribution and function in primitive systems. The major objectives will be to determine whether or not CA is central to a number of different biological processes in a wide variety of primitive organisms. This work should provide new and useful information on the origins and evolution of CA function and on the pattern of organization of cellular metabolic pathways in primitive systems.