Comparative properties of tobacco hornworm, Manduca sexta, carbonic anhydrases

Abstract

Comparative properties of midgut, fat body and integumentary carbonic anhydrases (CAs) were measured as functions of CA-catalyzed CO2 hydration or p-nitrophenylacetate (pNPA) hydrolysis in feeding larvae and pharate pupae. Alkali metal cations fully reverse the halide anion inhibition of CA catalyzed CO2 hydration during the larval but not the pharate pupal stages in development. Concentrations of acetazolamide required to inhibit 50% of tissue-specific CA-catalyzed CO2 hydration (I50) were approximately 10(-8) M. The activity profiles between pH 6.0 and 9.0 had well-defined optima around pH 8.0 with activity declining dramatically above the optima. When CA-catalyzed pNPA hydrolysis was measured between 4 and 37 degrees C, insect enzymes failed to exhibit positive Q10 values between 25 and 37 degrees C. The affinities of the hornworm CAs toward pNPA were determined with stage- and tissue-specific Km ranging from 0.42 to 8.0 X 10(-3) M. It is concluded that tissue and stage-specific CAs exist in M. sexta, whose properties appear to differ markedly with those previously reported for mammalian enzymes.