Properties of allophycocyanin II and its α- and β-subunits from the thermophilic blue–green alga Mastigocladus laminosus

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Abstract
Purified allophycocyanin II and its subunits were examined with respect to spectroscopic properties, sedimentation, reconstitution and isoelectric behavior. In 0.02 M-potassium phosphate buffer, pH 8.0, and at a concentration of 0.25 mg/ml, allophycocyanin II and its .alpha.- and .beta.-subunits show visible absorption maxima at 650, 615 and 615 nm, respectively, whereas the fluorescence emission maxima were determined to be at 662, 640 and 630 nm, respectively. The absorption difference spectrum (dilution difference) of allophycocyanin II displays maxima at 650 and 590 nm with a minimum at 610 nm. The c.d. spectrum of allophycocyanin II showed only 1 positive-ellipticity band at 635 nm, and a major negative-ellipticity band at 340 nm. Oxidation of allophycocyanin II, low- and high-pH solutions (pH 3.0 and 11.0), various ethanol concentrations as well as dialysis against distilled water induce a spectral change leading to phycocyanin-like characteristics. In most cases these shifts are reversible. Allophycocyanin II is thermostable over a period of 60 min at temperatures up to 60.degree. C. The isoelectric points of allophycocyanin II and its .alpha.- and .beta.-subunits are 4.65, 4.64 and 4.82, respectively. Estimated MW from sedimentation-equilibrium analyses were 102,500 for allophycocycanin II, 16,000 for the .alpha.- and 31,500 for the .beta.-subunit. Recombination of .alpha.- and .beta.-subunits leads to allophycocyanin II, which is indistinguishable from native allophycocyanin with respect to its spectral form, to its gel-filtration and to its electrophoretic behavior.