Carbonic anhydrase isozyme distribution and characterization in metabolic fiber types of the dorsal levator muscle of the blue crab, Callinectes sapidus

Carbonic anhydrase (CA) distribution and characterization were examined in white and light pink fibers of the dorsal levator muscle of the blue crab. White fibers were structurally and metabolically characterized as fast twit ch glycolytic, while the light pink fibers were fast oxidative. All subcell ular fractions of both fiber types had significant levels of CA activity; c ytoplasmic and microsomal activity was significantly higher in light pink v s white fibers. Cytoplasmic CA from both fiber types was highly sensitive t o the inhibitors acetazolamide and chlorzolamide, with Ki values of approxi mately 2 and 0.4 nM, respectively. Further analysis confirmed that cytoplas mic CA from both fiber types was kinetically similar to the high turnover T ype II isoform. It appears that the evolution of the CA Type III isoform, f ound in vertebrate red muscle, did not occur with the differentiation of me tabolic fiber types in crustaceans. Membrane-associated CA, which was also kinetically similar to the Type II isoform, was 20-fold higher in light pin k fibers, suggesting a physiological role in facilitated CO2 efflux from th e muscle fiber during periods of prolonged maximal activity. (C) 2001 Wiley -Liss, Inc.