AJP - Regulatory, Integrative and Comparative Physiology, Vol 241, Issue 1 92-R99, Copyright © 1981 by American Physiological Society
Comparative properties of tobacco hornworm, Manduca sexta, carbonic anhydrases
A. M. Jungreis, N. D. Barron and J. W. Johnston
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.
