Cyanophycin
Or Cyanophycingranaprotein cyanophycin ( CGP) is a biopolymer which is formed as a nitrogen molecule in the memory a series of cyanobacteria and bacteria, and placed in the cell. It was discovered in 1887 and consists of equal proportions of the amino acids L -aspartic acid and L- arginine. The use of this polymer is not yet, however, because of the polyacrylate very similar properties conceivable.
Physiology
Cyanophycin is formed by a number of cyanobacteria and some bacteria (eg Acinetobacter calcoaceticus ) as a storage material. It stores primarily nitrogen and carbon, and is used particularly for stationary, ie at the time of shortage of resources in the substrate, formed at the transition from exponential bacterial growth.
Properties and synthesis
Cyanophycin is composed of various types of cyanobacteria and may in these achieve a share of up to 18 percent of the dry cell mass. The polymer obtained has a molar mass of up to 125,000 g.mol - 1, and consists of a chain of repeating monomers of L- aspartic acid, which are linked via their free β - carboxyl group of the α -amino group in each case one molecule of L- arginine. There are also variations in the amino acid composition.
The formation of the polymer is independent of the ribosomes of the cell by the enzyme cyanophycin synthetase, which consists of two identical subunits each of 90 to 130 kDa. The enzyme needs as the starting polymer has a block of at least three monomers and ties under expenditure of energy by splitting each one molecule of adenosine triphosphate ( ATP) in this chain alternating the two amino acids. The polymer is first phosphorylated at the reactive end and the phosphate radical are substituted by the amino acid. Will affect the activity of the enzyme by the concentration of Mg2 and potassium chloride.
Research and production
So far, there is no large-scale production of the biopolymer. Cyanobacteria are suitable for various reasons for large-scale approaches, as they have for a very difficult -held demands on the substrate and on the other hand can provide only low yields of the polymer. Alternatives are the few bacteria that are able to form cyanophycin, especially Acinetobacter calcoaceticus. A strain of this bacterium accumulates the polymer with shares up 40 % of the cell dry weight. In addition, necessary for the formation of cyanophycin synthetase CPHA genes can be expressed in industrially relevant bacteria, especially in Escherichia coli, Corynebacterium glutamicum, Cupriavidus necator and Pseudomonas putida. These were brought to an optimized cyanophycin production by metabolic engineering. And the first method for the isolation of cyanophycin on an industrial scale have been developed.
Another approach to the production of cyanophycin is the use of green genetic engineering is to be applied to form cyanophycin in higher plants and to make as available. In the Federal Ministry of Food, Agriculture and Consumer Protection ( BMELV) funded project bsp was. the cyanophycin potatoes developed. In the potato a cyanobacterium Thermosynechococcus elongatus gene was inserted through which the plant is capable of a cyanophycin synthetase and thus form of the amino acids aspartate and arginine Cyanophycinzu. Other projects of the Federal Ministry of Education and Research (BMBF ) Effects of field trials of potato were investigated.
Reduction
So far, only a few studies on the biological degradation of cyanophycin have been carried out. Alexander Steinbüchel could identify as part of his research numerous Gram- negative and Gram- positive bacterial strains that degrade the polymer. In addition, he identified and isolated single facultative and strict ( obligate ) anaerobic bacteria that are able to take advantage of cyanophycin as the sole carbon and nitrogen source.