Physico-chemical and immunological properties of allophycocyanins

Cyanobacterial phycobilisomes. Particles from Synechocystis 6701 and two pigment mutants

The phycobilisomes of the unicellular cyanobacterium Synechocystis 6701, grown in white light, contain C-phycoerythrin, C-phycocyanin, and allophycocyanin in a molar ration of approximately 2:2:1, and in addition, polypeptides of 99, 46, 33.5, 31.5, 30.5, and 27 x 10(3) Daltons, as well as a trace of a approximately 9 x 10(3)-dalton component. Two nitrosoguanidine-induced mutants of this organism produce aberrant phycobilisomes. Crude cell extracts of these mutants, 6701-NTG25 and NTG31, contain phycoerythrin, phycocyanin, and allophycocyanin in a molar ration of 1:5:1:1 and 0.55:0.3:1.0, respectively. The phycobilisomes from both mutants lack the 33.5 x 10(3)-dalton polypeptide. Wile-type phycobilisomes consist of a core composed of an equilateral array of three cylindrical elements surrounded by six rods in a fanlike arrangement. The rods are made up of stacked disks, 11 nm in diameter and 6 nm thick. In phycobilisomes of mutant 6701-NTG25, numerous particles with fewer than six rods are seen. Mutant 6701-NTG31 produces incomplete structures that extend from triangular core particles, through cores with one or two attached rods, to cores with as many as five rods. The structure of the core appears unaltered throughout. The amount of phycocyanin (relative to allophycocyanin) appears to determine the number of rods per core. A common assembly form seen in 6701-NTG31 is the core with two rods attached at opposite sides. From observations of this form, it is concluded that the core elements are cylindrical, with a height of 14 nm and a diameter of 11 nm. No consistently recognizable structural details are evident within the core elements.

Wavelength modulation of phycoerythrin synthesis in Synechocystis sp. 6701

The spectral dependence of phycoerythrin synthesis has been studied in a unicellular photautotrophic cyanobacterium, Synechocystis sp. 6701, in which phycoerythrin synthesis alone is under chromatic control. Cells were partially depleted of their phycobiliprotein pigments through nitrate starvation in the light. Addition of nitrate to the culture medium allowed synthesis of phycobiliproteins in the dark. This synthesis occurred at the expense of the glycogen reserve accumulated during the period of nitrate starvation. Monochromatic irradiations of short duration at lambda less than 590 nm induced increased phycoerythrin synthesis during dark incubation. Monochromatic irradiations of short duration at lambda greater than 590 nm prevented this synthesis. These effects were photoreversible. The spectral distribution showed a maximum at 540 nm for the potentiation of phycoerythrin synthesis, and one at 640 nm for its photoreversal.

Some properties of allophycocyanin from a thermophilic blue-green alga

Allophycocyanin was purified from the extremely thermophilic blue-green alga Synechococcus lividus. It was shown to be more stable to thermal or urea denaturation than allophycocyanin from a mesophilic organisms. Its amino acid composition and spectroscopic response to pH were investigated. An analysis was made of the relatively low fluorescence polarization of allophycocyanin compared to that of a comparable sized aggregate of the biliprotein, C-phycocyanin. A rather speculative conclusion was reached that suggests that the lower polarization of allophycocyanin may be caused by orientations or positioning of the chromophores that are more favorable for intra-protein energy transfer.