| Abstrakt: |
The relative contribution of each functional carbonic anhydrase (CA) isozyme to liver CA activity of fed or starved adult male rats has been determined. The functional isozymes are CA II, CA III, CA IV, and CA V. Total CA, CA III, CA II, CA IV, and CA V activities (in mumol CO2 converted.min-1.liver-1), as measured by mass spectrometric assay using NaHC18O16O in aqueous solution at pH 7.4 and 37 degrees C, were 94,867, 38,621, 37,000, 14,515, and < 5,000 in fed rats and 40,630, 10,498, 9,137, 18,338, and < 2,600 in starved rats, respectively. CA II was unevenly distributed throughout the liver. In perivenous and periportal cytosols, as determined by the digitonin-pulse perfusion technique, CA II activity was (in mg cytosolic protein-1) 325 and 69 in fed rats and 167 and 33 in starved rats, respectively. CA III was more evenly distributed and less affected by starvation: CA III activity in perivenous and periportal cytosols was (in mg cytosolic protein-1) 84 and 55 in fed rats and 113 and 52 in starved rats, respectively. Evidence that CA III was concentrated in the nucleus was obtained histochemically by the Ridderstråle cobalt-precipitation technique in 2-microns-thick glutaraldehyde-fixed sections from adult fed rats. Liver CA activity was higher in the perivenous hepatocytes in cytosols and nuclei, whereas CA IV was homogeneously distributed. Incubation of the 2-microns sections with 1 microM acetazolamide resulted in inhibition of all membrane-associated CA, 50% of cytosolic CA, and no nuclear CA.(ABSTRACT TRUNCATED AT 250 WORDS) |
