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The chemical modification of beef liver catalase ec part 5 ethoxyformylation of histidine and tyrosine residues of catalase with di ethyl pyro carbonate

, : The chemical modification of beef liver catalase ec part 5 ethoxyformylation of histidine and tyrosine residues of catalase with di ethyl pyro carbonate. Journal of Biochemistry (Tokyo) 80(2): 229-237

In order to elucidate the possible roles of histidine and tyrosine residues of catalase [EC] in maintaining the quaternary structure and catalytic activity, diethylpyrocarbonate modification experiments were carried out. A method for the estimation of N-ethoxyformyl (EF)-His at pH 5-7 and of 0-ethoxyformyl (EF)-Tyr in alkaline solution by measuring A242nm (.epsilon.mM = 3.2) and A278nm (.epsilon.mM = 1.16), respectively, was developed. The formation of EF-His and EF-Tyr was an electrophilic reaction and was dependent on pH, exhibiting pK values of 6.8 and 9.9, respectively. The maximal yield of EF-His at pH 6.0 was 49% of the total histidine content, but no inactivation or unfolding of the enzyme was observed. The formation of 12 EF-Tyr residues/mol of catalase at pH 8.1 did not cause any inactivation, but the formation of 8 more EF-Tyr residues at pH 8.9 resulted in inactivation and unfolding. Nearly complete inactivation and partial splitting of catalase were observed when 43-46 EF-Tyr residues/mol were produced at pH 10.0. More EF-His residues were formed by the reaction of diethyl pyrocarbonate with cyanoethylated (CE)-catalase monomer (subunit) than with CE-catalase tetramer. The CE-catalase tetramer and monomer were extensively O-ethyoxyformylated, reaching 100% EF-Tyr formation. Half of the histidine residues apparently lie outside the protein core, with 3/4 of the tyrosine residues within the protein core of the enzyme. The production of 2-3 EF-Tyr residues/mol of the monomer by ethoxyformylation at pH 7.0 was accompanied by a decrease in the magnitude of the Soret peak. A possible interaction of those tyrosine residues with porphyrin of the heme group is discussed.


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