Abstract
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 β-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.