XXXX . Comparison of properties of solubilized mitochondrial and cytoplasmic activities.

@entity550 @entity6000 @entity4859 @entity8851 @entity413 @entity4337 @entity855
1. @entity550 , after purification by using high-density sucrose solutions, were extracted with @entity6000 . The total hexokinase activity of the intact mitochondria was increased by 50-80% in the Triton extracts. 2. @entity6000 was removed from mitochondrial extracts by a combination of @entity4859 fractionation and DEAE-cellulose chromatography. Mitochondrial hexokinase remained soluble after removal of extractant. 3. The behaviour of solubilized mitochondrial hexokinase was compared with soluble cytoplasmic hexokinase from the same samples of cerebral cortex on identical columns of @entity8851 -cellulose. Two peaks were eluted from each source of hexokinase. The distribution between hexokinase peaks was similar for the two sources. Peak I (approx. 80% of the total hexokinase) from each was eluted at identical concentrations of @entity4337 and slight differences were observed in the elution profiles for peak II. 4. The purified mitochondrial hexokinase showed the following kinetic properties: peak I, K(m)( @entity855 ) 0.60mm, K(m)( @entity413 ) 0.042mm; peak II, K(m)( @entity855 ) 0.66mm, K(m)( @entity413 ) 0.043mm. The purified cytoplasmic hexokinase Michaelis constants were: peak I, K(m)( @entity855 ) 0.56mm, K(m)( @entity413 ) 0.048mm; peak II, K(m)( @entity855 ) 0.68mm, K(m)( @entity413 ) 0.062mm. 5. Although no significant differences between mitochondrial and cytoplasmic hexokinases were noted in chromatographic behaviour or in the kinetic properties studied, the purified mitochondrial enzyme was activated slightly (approx. 20%) by @entity6000 , in contrast with the cytoplasmic enzyme, which was not affected. 6. The results, taken to indicate basic similarity between mitochondrial and cytoplasmic hexokinases, are discussed in relation to the role of the two sources of enzyme in the metabolism of the tissue.
