Infection of Agaricus bisporus with Pseudomonas tolaasii or treatment with a tolaasin containing preparation resulted in the activation of tyrosinase and the development of a brown discolouration of the fruitbody. In order to investigate whether tolaasin is responsible for these reactions, mushrooms were treated with different concentrations of HPLC-purified tolaasin. Tolaasin was found to induce both browning and the activation of tyrosinase, with the level of activation being related to the concentration of toxin applied. In water-treated controls, active tyrosinase isoforms with pIs of 4.5 and 4.4 were the main isoforms found but tolaasin treatment resulted in the activation of a tyrosinase isoform with a pI of 5.7. The different active isoforms could be distinguished as the tolaasin activated isoforms had a higher affinity for catechol as a substrate (K(m) 0.82 mM) than the active isoforms in the control (K(m) 2.86 mM). In mushrooms inoculated with P. tolaasii or treated with tolaasin containing extracts no significant differences were found in the mechanism of oxidation of tyrosine, γ-glutaminyl-4-hydroxybenzene or γ-glutaminyl-3,4-dihydroxybenzene to form melanin. In tolaasin treated samples, a constant total amount of melanin and sum of the three phenols was found.
Soler Rivas, C., Arpin, N., Olivier, J. M., & Wichers, H. J. (1999). The effects of tolaasin, the toxin produced by Pseudomonas tolaasii on tyrosinase activities and the induction of browning in Agaricus bisporus fruiting bodies. Physiological and Molecular Plant Pathology, 55(1), 21-28. https://doi.org/10.1006/pmpp.1999.0200