Detection of natural and induced phenoloxidase activities in human serum

Natural and induced phenoloxidase activities were detected in human serum using nine different phenolic substrates, namely, tyrosine, tyramine, L-DOPA, DL-DOPA, dopamine, catechol, hydroquinone, protocatechuic acid and pyrogallol. Phenoloxidase activity was induced anew in serum using exogenous elicitors, such as proteases or detergents. Among the proteases and detergents tested, pronase, SDS and Tween 20 were the best elicitors of phenoloxidase activities in serum, wherein, hydroquinone was the best phenolic substrate for both untreated as well as pronase treated serum and SDS or Tween 20 treated serum resulted in highest oxidation of dopamine or tyrosine, respectively. In the present study, all these oxidative reactions were inhibited by phenoloxidase inhibitors, namely, PTU and tropolone, thereby, confirming the role of phenoloxidase in human serum.