Potent reversible, competitive inhibitor of tyrosinase (phenol oxidase) in the nanomolar range. Monomer. POI activity increases throughout pupariation, and is highest in final instar pupae. No activity in newly emerged adults. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Contains L-DOPA (3',4'-dihydroxyphenylalanine).