Photochemical effects associated with the copper absorption bands of the native hemocyanin from Octopus vulgaris

Emission spectra from copper proteins containing type-3 centres

Aqueous solutions of copper-proteins containing type-3 centres (ceruloplasmin, tyrosinase, haemocyanin), excited within their absorption bands at 325-345 nm, show typical luminescence spectra. The emission bands peak at 415-445 nm and their decay time is no longer than 10 ns. A strong analogous fluorescence is obtained also by excitation of concentrated solutions of carboxylic acids and amino acids, which show again absorption bands around 330 nm. Such a fluorescence, although less intense, is also observed in copper(II) carboxylate solutions. In contrast, no fluorescence has been recorded in solutions of acetic anhydride and of polypeptides (valinomycin, gramicidin D), which do not have free carboxyl groups. We tentatively attribute this novel fluorescence in the investigated copper proteins to interactions between carboxyl groups of amino acids at, or near, the active site.

[Spectroscopic study of the structural changes of scorpion hemocyanin, induced by pH variations and addition of various salts]

Structural modifications of the scorpion haemocyanin induced by pH variations and salt addition are studied by U.V. absorption, fluorescence, circular dichroism and light scattering. Haemocyanin fluorescence is due to both aromatic amino-acids tyrosine and tryptophan. Deoxygenation or denaturation lead to a fourfold enhancement of its intensity. At acidic pH the active site is modified and the protein is dissociated, but at alkaline pH the haemocyanin aggregates. The addition of different salts (sodium citrate, potassium bromide and iodide...) involves protein dissociation, the amplitude of which depends on the anion. But pH variations and salt addition don't change the haemocyanin secondary structure as shown by circular dichroism. The C.D. spectrum of scorpion haemocyanin exhibits the characteristic bands of Arthropod haemocyanine.