What follows is a brief introduction to Haemocyanin.
Haemocyanin is the most widely distributed of the respiratory pigments after haemoglobin, and is found in members of the molluscs and the arthropods.
Haemocyanin contains copper rather than iron.
The name Haemocyanin comes from it’s characteristic blue colour, produced when one molecule of oxygen binds to the two copper atoms.
Both molluscan and arthropod haemocyanins are not confined to corpuscles but are dissolved freely in the haemolymph.
Despite similar physiological roles molluscan and arthropod haemocyanin, structurally the two haemocyanins have very little in common.
Amongst the arthropods, haemocyanin is found in the Chilopoda (eg the centipedes), the Chelicerata (in both the Arachnida (spiders and scorpions) and Merostomata (horseshoe crabs)), and in Crustacea (decapods, isopods, amphipods and stomatopods).
The haemocyanin of arthropods is constructed from loosely linked subunits. Each subunit having one active site (containing two copper atoms) binding one oxygen atom.
Very few of the haemocyanins however have a single type of subunit, with most species having four or possibly more different types.
In arthropods the basic aggregation state is the hexamer which may exist alone in the haemolymph, such as in the amphipod Orchestia gammarellus. However in many of the arthropods higher aggregates constructed from the basic hexameric assembly also occur. For many crabs and lobsters, haemocyanin occurs as a mixture of hexamers and dodecamers, with the latter predominating . For the shore crab Carcinus maenas it is the dodecamer form that dominates with a minor amount of hexamer present.
There is considered to be a physiological significance in the ratio of dodecamer to hexamer, as formation of dodecamers may influence the oxygen-binding properties of the protein as well as minimizing the colloidal osmotic pressure of the haemolymph and facilitating primary urine function .
The aggregation state of haemocyanin has been shown to be influenced by salinity, temperature and the protein concentration of the haemolymph in the mud shrimp Callianassa californiensis, as well as by differences in salinity and moult stage in Carcinus maenas.
