VARIATIONS IN THE AMINO-ACID-COMPOSITION OF CYANOPHYCIN IN THE CYANOBACTERIUM SYNECHOCYSTIS SP PCC-6308 AS A FUNCTION OF GROWTH-CONDITIONS

Gas chromatography-mass spectrometry studies of the nitrogen isotopic composition of the N-trifluoroacetyl n-butyl ester derivatives of the amino acids from isolated hydrolyzed cyanophycin from N-15-enriched ce lls led to two major findings: (1) the amino acid composition of this granular polypeptide, isolated using procedures optimized for extracti ng and purifying cyanophycin from cells in the stationary growth phase , varied with the culture growth condition; (2) the rate of incorporat ion of exogenous nitrate differed for each nitrogen atom of the amino acid constituents of cyanophycin or cyanophysin-like polypeptide. Argi nine and aspartic acid were the principle components of cyanophycin is olated from exponentially growing cells and from light-limited station ary phase cells, with glutamic acid as an additional minor component. The cyanophycin-like polypeptide from nitrogen-limited cells contained only aspartic and glutamic acids, but no arginine. The glutamic acid content decreased and arginine content increased as nitrate was provid ed to nitrogen-limited cells. These cells rapidly incorporated nitrate at different rates at each cyanophycin nitrogen site: guanidino nitro gens of arginine > aspartic acid > a-amino nitrogen of arginine > glut amic acid. Little media-derived nitrogen was incorporated into cyanoph ycin of exponentially growing cells during one cellular doubling time.