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Phosphate-limited growth of the blue-green alga Agmenellum quadruplicatum resulted in the accumulation of cyanophycin granule polypeptide (CGP), which is a 1:1 co-polymer of aspartic acid and arginine. The progressive accumulation of CGP began after depletion of phosphate from the medium. CGP increased in concentration much faster than the increase in cell number. Electron microscopy indicated that both the number of cyanophycin granules per cell section and the diameter of each granule increased as phosphate starvation progressed. A marked decrease in the electron density of the inter-thylakoidal areas took place concurrently with the accumulation of CGP. At the same time a progessive decrease in the pigment concentration of cells and in the rate of nitrate uptake was observed. Thirty-two hours after phosphate depletion from the medium up to 28% of total cellular nitrogen was found in CGP.Cyanophycin or structured granules have been observed in thin sections of several cyanobacteria (1,6,8,(10)(11)(12)

The level of glutamine synthetase activity in Agmeneihm quadruplicatum strain Most of the work on the nitrogen metabolism of PR-6 has centered on studying mutants with lesions in the reduction of N03-or N02 (20, 22-24). These studies led to the conclusion that the reduction of NO03 to N02 was tightly regulated by NH3 (22,23

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