Sclerotization of the perisarc of the calyptoblastic hydroid, Laomedea flexuosa 2. Histochemical demonstration of phenol oxidase and attempted demonstration of peroxidase.

Histoehemical evidence is presented that cells, described as 'tanning cells', in the hydroid Laomedea flexuosa contain an orthodihydroxyphenol oxidase and transfer this enzyme to the perisarc. The detection of copper in the tanning cells provides further evidence for the presence of phenol oxidase, a copper-containing enzyme. Evidence is presented that this enzyme and the orthodihydroxyphenol, dopamine, are stored together in the same 1mu diameter spherical inclusions. The enzyme and orthodihydroxyphenolic substrate appear to be transferred together to the perisarc where it is thought that the dopamine is oxidized by the phenol oxidase to produce a quinone. The quinone is thought to cross-link the structural proteins to form a strong, inert exoskeleton, the perisarc. Attempts to demonstrate peroxidase using benzidine methods are also described. Both the spherical inclusions of the tanning cells and the perisarc of the hydrothecae give a reaction with benzidine in the absence of hydrogen peroxide. This suggests the presence of an oxidizing agent which is not a peroxidase but is possibly a quinone.