Multiple forms of phycoerythrin-545 from Cryptomonas maculata

Abstract

Three multiple phycoerythrin-545 forms were purified from crude extracts of Cryptomonas maculata by preparative isoelectric focusing. The phycoerythrin forms are charge isomers with isoelectric points at 7.83, 5.05 and 4.84. The multiple pigment forms have similar molecular weights of 44500 daltons and are composed of subunits of unequal size in a 1:1 stoichiometry with molecular weights of (α) 9900 and (β) 15700 daltons, twice. The proposed quarternary structure of the native pigments is (α)₂(β)₂.

The charge differences of the phycoerthrins are caused by a charge heterogeneity of the light α subunits, as revealed by urea gel electrophoresis. The α chains of pigment form pI 7.83 had a greater electrophoretic mobility than those α subunits of the acidic pigment forms pI 5.05 and pI 4.84.

The phycoerythrin forms have an absorption spectrum with similar absorption maxima at 544 nm, but differ in the position of the long wavelength shoulders lying at 555 and 557 nm in the negatively charged pigment forms and at 560 nm for the phycoerythrin form with a pI at 7.83.

The fluorescence emission spectra coincide in their asymmetrical shape with shoulders at about 620 nm; they slightly differ int he position of the emission maxima at 586 nm for the phycoerythrins with pIs at 4.84 and 5.05 and at 584 nm for phycoerythrin with pI at 7.83.