Summary: A system was developed for the formation of ethylene by an extract of pv. PK2. The ethylene-forming activity of a cell-free extract of this bacterium measured in a system reported previously was almost completely lost when the cell-free extract was dialysed against potassium phosphate buffer for 24 h at 4 °C. When the fraction of cell-free extract with a molecular mass < 10 kDa (SupI) was added back to the enzyme fraction after gel filtration of the cell-free extract, the enzymic activity increased to about four times that of the gel-filtered crude enzyme. The action of SupI could be reproduced by the addition of l-arginine. The complete system for the formation of ethylene under aerobic conditions required 0·25 mm-2-oxoglutarate, 0·2 mm-FeSO, 2 mm-DTT, 10 mm-l-histidine and 0·2 mm-l-arginine. The cofactor specificity was examined by replacing l-arginine or l-histidine with various analogues, but none of them were effective. The components of this system, with the exception of l-histidine, were similar to those of a system derived from the ethylene-producing, plant pathogenic fungus which also produced ethylene in a reaction dependent on 2-oxoglutarate. The intermediates in the ethylene-forming reaction are postulated and the roles of l-arginine and l-histidine in the formation of ethylene by are discussed.


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