Cyanide formation in preparations from Chlorella and New Zealand spinach leaves: Effect of added amino acids.

As part of an effort to identify the natural precursor(s) of HCN in the alga Chlorella vulgaris Beijerinck, and in leaves of New Zealand spinach (Tetragonia expansa, Murr.), HCN release was measured after addition of various amino acids to illuminated algal extracts and grana preparations. Histidine is particularly effective as an HCN precursor, both with Chlorella extracts and leaf grana. With the algal extracts, D-histidine is about ten times more effective than L-histidine and histamine, whereas the two isomers (and histamine) are about equally effective with leaf grana. In the presence of leaf grana plus added Mn(2+) and peroxidase, L-tyrosine and L-cysteine like-wise cause HCN formation; but these amino acids cause little or no HCN formation in the presence of Chlorella extracts. A stimulation of HCN production by L-histidine was observed with intact Chlorella cells. Because of the limitations of the assay method, the possibility can not be excluded that other substances than histidine may also lead to HCN generation in Chlorella vulgaris, but the results show that histidine has an important role in HCN generation by this species.