The dark respiration of Anacystis nidulans. Production of HCN from histidine and oxidation of basic amino acids.

The basic amino acids, L-arginine, L-lysine, LO-irnithine, and to a lesser extent L-histidine, strongly stimulate the O2 uptake of cell suspensions of the blue-green alga or cyanobacterium anacystis nidulans. In the case of L-histidine, the extra O2 consumption is associated with the formation in vivo of small amounts of HCN, particularly in an atmosphere of O2. The enzyme responsible for both the stimulated O2 uptake with the basic amino acids and the formation of HCN from histidine has been isolated and identified as an L-amino acid oxidase specific for the basic amino acids. The purification (15 000-fold) of this enzyme is described. The isolated enzyme is inhibited by o-phenanthroline, which has a similar inhibitory effect on the O2 uptake of cell suspensions with (and without) added amino acids. The basic amino acid oxidase, which is not inhibited by HCN, can be regarded as an 'alternate' oxidase in A. nidulans. An oxidase sensitive to HCN is apparently also operative. At high concentrations of lysine or arginine added HCN can almost double the initial rate of O2 consumption of cell suspensions. This can be attributed to the inhibition of catalase by HCN. At low concentrations of the amino acids, and with more prolonged incubation time, HCN becomes inhibitory. One interpretation could be that the HCN-sensitive terminal oxidase is also involved in the extra O2 uptake elicited by the basic amino acids, but other interpretations are possible. The extra O2 uptake elicited by histidine is almost completely inhibited by HCN, which is consistent with the finding that histidine is a relatively poor substrate for the basic amino acid oxidase.