Penaeus monodon (tiger shrimp) hemocyanin: Subunit composition and thermostability

Penaeus monodon (class Crustacea, order Decapoda) is one of the largest shr imps of the Penaedea family from the Indo - West Pacific region. The dioxyg en-transporting protein hemocyanin, isolated from the hemolymph of this inv ertebrate, is composed of three 75-76 kDa structural/functional subunits de signated as Pm1, Pm2 and Pm3. The N-terminal sequences of the chains were d etermined and compared with those of other decapodan hemocyanin subunits. P m2 and Pm3 art: highly homologous and electrophoretically undistinguishable polypeptides. In comparison to Pml, they have an extension of six residues . Pml is closely related to the subunit Pv2 of the Penaeus vannamei hemocya nin. Probably, subunits like Pml and Pv2 are family-specific for the Penaei dea hemocyanins and the other subunits are species-specific. Comparison of N-terminal sequences of respiratory proteins from the sub-orders Natantia a nd Reptantia demonstrated family- and sub-order-specific sequences. A melting point of 69 degreesC, lower than those for the di-hexameric decap odan hemocyanins, was determined from the temperature dependence of ellipti city of the mono-hexameric Penaeus monodon hemocyanin. Thermostability of d ecapodan hemocyanins depends on their aggregation state.