A Study on Esterase Activity of Carbonic Anhydrase from Van Lake Fish (Calcalburnus tarichi)


Abstract: No study has been reported on carbonic anhydrase enzyme of the fish (Calcalburnus tarichi) living in the carbonated Van Lake. Having partial purification of Carbonic anhydrase from gill and liver of Van Lake fish by ethanol-chloroform and acetone-chloroform, the esterase activity was performed by using p-nitrophenyl acetate as a substrate on spectrophotometer. The effects of the some kinetic parameters (km, Vo, Vmax, Na_2CO_3 activation, optimum pH etc.) have been examined When Lineweaver-Burk diagram of liver extracts (at 25°C) is examined, ethanol has an apparent competitive inhibition compare to acetone extracts. So Km of the substrate (p-nitrophenyl acetate) is 0.95 mM is for ethanol extract and 0.54 mM of that is found for acetone extracts. In two extracts from gill (at 25°C), ethanol seems to have a non-competitive inhibition comparing to acetone, Km for both extracts is 0.39 mM. Na+/CO_3^{2-} ions induce esterase activity, Na+/CO_3^{-2} ions are not competitive with the inhibitory effects of ethanol. Infect, inhibition of ethanol on gill esterase activity appears to be competitive which is understood by addition of Na+/CO_3^{-2}. Since carbonate ions and p-nitrophenyl acetate act on two different catalytic site of this enzyme, both have formed a cooperative effect It is clear that carbonic anhydrase activity has not been affected till pH:7.4. Although pH above 8.0 enzyme activity has seem to increase, this increase is due to kinetic reaction between substrate (p-nitropheny acetate) and buffer at pH:8-11.5. So, the esterase activity of this enzyme at this high pH, can not be evaluated. for the esterase activity of this enzyme. The optimal and unaffected pH for the substrate is 7 for the esterase activity of carbonic anhydrase. "Esterase" activity could be useful for determining "anhydrase" activity of Carbonic anhydrase enzyme of Van Lake fish. Stimulation of esterase activity of carbonic anhydrase has been shown by addition of CO_3^{2-} ions. Carbonic anhydrase present in gill and liver of Van Lake fish has a significant regulatory role for internal pH balance.

Keywords: Carbonic anhydrase, Van Lake fish, esterase activity

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