A protein from leaves catalysing the reduction of haem–protein compounds by illuminated chloroplasts

Abstract

It was shown previously (Davenport, Hill & Whatley, 1952) that extracts of leaves contain a factor capable of catalysing the reduction of methaemoglobin and metmyoglobin by illuminated chloroplasts. Although this hydrogen-transferring capacity appeared to be analogous to that of ferric oxalate in a similar system (Hill & Scarisbrick, 1940), the naturally occurring substance was shown to be thermolabile, non-diffusible and stable only between the limits pH 5-0-9 0. Attempts at purification by fractional precipitation with ammonium sulphate gave active precipitates at near-saturation with the salt. It was concluded that the methaemo- globin-reducing activity was associated with a protein fraction of the leaf. In the earlier investigation it was found that the preparations of the factor were too unstable to allow a purification sufficient for characterization. It has now been found that if the leaves are held in a frozen state before ex- traction, the stability of the preparations was con- siderably improved and a highly purified product could be obtained. More recently (Hill, Northcote & Davenport, 1953) a similar activity was detected in cell-free extracts of the alga Chlorella. The present paper is concerned with the further purification of the 'methaemoglobin-reducing factor' and some additional properties are described. A brief account of this work was published previously (Davenport & Hill, 1955).