The activation reaction of prophenoloxidase was analyzed using a homogeneous pro-enzyme preparation and highly purified pro-phenoloxidase activating enzyme (abbreviated as PPAE) obtained from silkworm larvae. The activation of pro-enzyme by PPAE results in release of a peptide having a molecular weight of about 5000 calculated from its amino acid composition and the difference between the molecular weights of the pro-enzyme and phenoloxidase. PPAE seems to be a highly specific enzyme capable of limited proteolysis, since no further degradation of phenoloxidase or release of any other peptide could be detected. Phenoloxidases having different kinetic properties and substrate specificities were obtained depending on the pH at which activation took place, although the molecular weights of phenoloxidase determined by sodium dodecylsulphate-electrophoresis were the same irrespective of the operating pH. This suggests that a process subsequent to peptide bond cleavage in the activation reaction is influenced by pH, resulting in phenoloxidases with different properties. Phenoloxidase seems to be present as progressively higher molecular weight aggregates. The enzyme is bound strongly to foreign surfaces such as glass, DEAE-cellulose and hydroxyapatite, from which much of the enzyme activity cannot be eluted by high NaCl or phosphate concentration. This may be important in relation to the intracellular binding and occurrence of multiple forms of phenoloxidase. © 1980.
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