The distribution of carbonic anhydrase type I and II isozymes in lamprey and trout: possible co-evolution with erythrocyte chloride/bicarbonate exchange |
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Authors: | Raymond P Henry Bruce L Tufts Robert G Boutilier |
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Institution: | (1) Department of Zoology, Auburn University, 101 Cary Hall, 36849-5414 Auburn, AL, USA;(2) the Alabama Agricultural Experiment Station, Auburn University, 101 Cary Hall, 36849-5414 Auburn, AL, USA;(3) Department of Biology, Queens University, K71 3N6 Kingston, Ontario, Canada;(4) Department of Zoology, University of Cambridge, Downing Street, CB2 3EJ Cambridge, UK |
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Abstract: | The subcellular distribution and kinetic properties of carbonic anhydrase were examined in red blood cells and gills of the lamprey, Petromyzon marinus, a primitive agnathan, and rainbow trout, Oncorhynchus mykiss, a modern teleost, in relation to the evolution of rapid Cl–/HCO
3
–
exchange in the membrane of red blood cells. In the lamprey, which either lacks or has minimal red cell Cl–/HCO
3
–
exchange, there has been no compensatory incorporation of carbonic anhydrase into the membrane fraction of either the red cell or the gill. Carbonic anhydrase activity in red cells is exclusively cytoplasmic, and the single isozyme displays kinetic properties typical of the type I, slow turnover, isozyme. In the red blood cells of the trout, however, which possess high amounts of the band-3 Cl–/HCO
3
–
exchange protein, the single carbonic anhydrase isozyme appears to be kinetically similar to the type II, fast turnover, isozyme. It thus appears that the type I isozyme present in the red blood cells of primitive aquatic vertebrates was replaced in modern teleosts by the kinetically more efficient type II isozyme only after the incorporation and expression of a significant amount of the band-3 exchange protein in the membrane of the red cell.Abbreviations BCIP
5-bromo-4-chloro-3-indolyl phosphate
- CA
carbonic anhydrase
- DTT
dithiothreitol
- EDTA
ethylenediaminetetra-acetate
-
E
0
total concentration of free enzyme
-
i
fractional inhibition of enzyme activity
- IU
international units
-
K
1
inhibition constant
-
K
M
Michaelis constant
- NBT
nitro blue tetrazolium
- NCP
nitrocellulose paper
- RBC
red blood cell
- SDS-PAGE
sodium dodecyl sulphate polyacrylamide gel electrophoresis
-
V
max
maximal velocity of reaction |
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Keywords: | Carbonic anhydrase Cl/HCO3 exchange Red blood cells Lamprey Petromyzon Trout Oncorhynchus |
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