Location of intrinsic and inducible phenoloxidase activity in molluscan hemocyanin.
The phenoloxidase (PO) activity of the hemocyanins (Hcs) from two molluscan species, the gastropod Helix pomatia (Hp) and the cephalopod Sepia officinalis (So), was studied. With catechol as substrate the Hcs showed a weak o-diPO activity, which was moderately enhanced on limited proteolysis with subtilisin. The sites in the Hc molecules mainly responsible for this activity were identified. The highest intrinsic o-diPO activity and also by far the highest level of induction were found in the functional units (FUs) Hp f and So g, isolated from Hp beta-Hc and So Hc (subunit 2), respectively. The results thus support the earlier conclusion, made on the basis of sequence homology between molluscan Hcs, that Hp f and So g are functional and structural analogues. The subtilisin treatment of Hp f also induced monoPO activity, considered to be at the origin of browning of the sample.
Siddiqui
Nurul Islam
NI
Laboratory of Biochemistry, Chemistry Department, Katholieke Universiteit Leuven, Celestijnenlaan 200 G, 3001 Leuven-Heverlee, Belgium.
Akosung
Roland Forben
RF
Gielens
Constant
C
D000818:Animals; D002384:Catalysis; D004789:Enzyme Activation; D004790:Enzyme Induction; D006372:Helix, Snails / Q000201:enzymology*; D006433:Hemocyanins / Q000737:chemistry* / Q000378:metabolism; D014442:Monophenol Monooxygenase / Q000096:biosynthesis* / Q000378:metabolism; D010084:Oxidation-Reduction; D017434:Protein Structure, Tertiary; D049833:Sepia / Q000201:enzymology*
D006433:Hemocyanins; D014442:Monophenol Monooxygenase