Penaeus monodon (class Crustacea, order Decapoda) is one of the largest shrimps of the Penaeidea family from the Indo-West Pacific region. The dioxygen-transporting protein hemocyanin, isolated from the hemolymph of this invertebrate, is composed of three 75-76 kDa structural/functional subunits designated as Pm1, Pm2 and Pm3. The N-terminal sequences of the chains were determined and compared with those of other decapodan hemocyanin subunits. Pm2 and Pm3 are highly homologous and electrophoretically undistinguishable polypeptides. In comparison to Pml, they have an extension of six residues. Pm1 is closely related to the subunit Pv2 of the Penaeus vannamei hemocyanin. Probably, subunits like Pm1 and Pv2 are family-specific for the Penaeidea hemocyanins and the other subunits are species-specific. Comparison of N-terminal sequences of respiratory proteins from the sub-orders Natantia and Reptantia demonstrated family- and sub-order-specific sequences. A melting point of 69 degrees C, lower than those for the di-hexameric decapodan hemocyanins, was determined from the temperature dependence of ellipticity of the mono-hexameric Penaeus monodon hemocyanin. Thermostability of decapodan hemocyanins depends on their aggregation state.

Amino Acid Sequence↗

PubMedDate not supplied

Viviparus ater hemocyanin: investigation of the dioxygen-binding site and stability of the oxy- and apo-forms.

The active site of Viviparus ater (mollusc) hemocyanin was investigated using the fact that the binding of dioxygen to the binuclear copper-containing sites of hemocyanins is connected with the appearance of specific dichroic bands which are very sensitive to changes in the structrure and polarity of the environment. Oxy-Viviparus ater hemocyanin exhibits near UV and visible circular dichroism spectra different from those of other molluscan and arthropodan hemocyanins. These differences are due probably to variations in the geometry or charge distribution in the dioxygen binding sites of the compared proteins. The thermostability of Viviparus ater hemocyanin and the significance of the copper-dioxygen system for the stability were also investigated. "Melting" temperatures, Tm, of 77 degrees C for the oxy-hemocyanin and 57 degrees C for the apo-protein were calculated from the denaturation curves which demonstrates the considerable role of the binuclear active site for the thermostability. Viviparus ater hemocyanin is more thermostable than other hemocyanins for which data are published.

Amino Acids↗