The difference of the structure of the cell membrane and the cell wall to different groups of microorganisms, algae, bacteria, fungi and cyanobacteria leads to a significant difference concerning the mechanisms of metal binding to the cellular components. Thus, most of microelements, as a result of entering the cyanobacterial cells, form bonds with the molecules of organic compounds as proteins, lipids, polysaccharides, amino acids etc. If the microelements are in excess they are stored in specific configurations being stored in inactive and non toxic form for the cell. The absorption capacity of heavy metals by cyanobacteria is mainly due to the protein-COO- groups and the secondary functional chains of amino acids such as histidine, cysteine, aspartic acid and glutamic acid. The histidine and carboxylic group effectively bind Cu(II) because of its bidentate structure. The copper, in high quantities being toxic and penetrating into the cell, forms complexes with proteins as the free ion can cause the oxidative stress and leads to the lipids oxidation and macromolecules degeneration. The obtained results concerning the copper accumulation in the biomass of Spirulina showed interest to study with what organic components of the biomass the intracellular accumulated copper was bound. The fractionation method of the biomass of Spirulina was based on the solubility of the cellular constituents in different solvents combining some of the known and described methods. Thus, as a result of Spirulina biomass fractionation cultivated in the presence of the compounds [Cu(L9-2H)] and [Cu(L11-H)Br] in a concentration of 2.00 and 6.00 mg/L respectively, compounds that lead to the maximum accumulation of copper in Spirulina biomass (10.63 and 11.14 mg%), it proved that the total amount of copper accumulated in the biomass, the most important weight of copper is due to the fraction of carbohydrates and peptides with amino acids (Figure 1).   Fig. 1. Distribution of copper in fractions extracted from Spirulina biomass cultivated in the presence of 2.00 mg/L – [Cu(L9-2H)] and 6.00 mg/L – [Cu(L11-H)Br] As a result of the fractionation of Spirulina biomass cultivated in the presence of the compound [Cu(L9-2H)] it was known that from the total amount of copper accumulated in the biomass, the highest content of copper was bound with the fraction of peptides and amino acids – 30.10% (3.20 mg%) and the carbohydrates fraction – 28.22% (3.00 mg%). The copper incorporated into protein molecules represents 26.25% of the total copper and the most decreased content was detected in the lipid fraction and constitutes about 15.99% of the total copper in the biomass. The researches carried out in the cultivation of Spirulina in the presence of coordination compound [Cu(L11-H)Br] have shown that the accumulated copper content is 11.14 mg% from ADB. The maximum weight of copper is due to the carbohydrates and peptides fraction with amino acids constituting 31.42% (3.5 mg%) and 27.29% (3.04 mg%), respectively, from the total copper, followed by the lipid fraction – 25.58% (2.85 mg%). In the case of Spirulina cultivation in the presence of the coordination compound of copper [Cu(L11-H)Br], the protein molecules from Spirulina biomass bind a smaller amount of copper compared to the compound [Cu(L9-2H)] and constitute 15.71% (1.75 mg%) of the total copper accumulated in the biomass.