EFFECTS OF POLYPHOSPHATES ON REACTIONS OF METMYOGLOBIN RELATED TO OXIDATIVE CHANGES IN MEAT-PRODUCTS

Diphosphate, triphosphate and trimetaphosphate stabilize the haem cavi ty in metmyoglobin (MMb), as evidenced by an absorption increase in th e Soret band, while only triphosphate and trimetaphosphate decrease th e rate of MMb-catalysed oxidation of linoleic acid as monitored by oxy gen consumption. It is suggested that the larger triphoshate and trime taphosphate most effectively hamper access of lipid substrates to the iron (III) in the haem cavity, protecting both the MMb and to a lesser extent the fatty acid against oxidative degradation. Further indicati on of a weak but specific interaction between the polyphosphates and t he haem cavity of MMb was found in an increase in the rate of enzymati c reduction of MMb to oxymyoglobin, most significantly by trimetaphosp hate, and in a lowering of the acidity of the water co-ordinated to ir on (III) in MMb (pK(a) = 8.83 with added polyphosphates, and pK(a) = 8 .52 without added polyphosphates, 25-degrees-C, extrapolated to zero i onic strength).