Abstract
The enzyme, phenoloxidase, was isolated and partially purified as an inactive enzyme, a proenzyme, from plant cell cultures of Daucus carota, Nicotiana tabacum, and Haplopappus gracilis. The prophenoloxidase was found to be specifically activated by Ca(2+) or Mn(2+) ions in concentrations above 1 millimolar. Calmodulin was not involved in this activation. Concentrations of Ca(2+) or Mn(2+) below 1 millimolar could not induce activation of the prophenoloxidase, but if trypsin was added simultaneously with Ca(2+) or Mn(2+) at a concentration of 1 millimolar or below, the proenzyme was converted to its active form. The inactive form of phenoloxidase was found to be a soluble enzyme, whereas after activation the enzyme aggregated, and a significant amount of the enzyme activity could become pelleted.