Contribution of cytoplasmic enzymes to apparent heterogeneity of rat brain mitochondria.

The results of this investigation indicate that there is sufficient contamination of washed primary rat brain mitochondrial preparations with cytoplasmic enzymes to cause possible misinterpretation of mitochondrial heterogeneity after isopycnic sucrose density gradient centrifugation, when based solely on enzyme activity measurements. Most of the contamination may be removed by a single 30 min centrifugation using the 3-6 % discontinuous Ficoll gradient method of Clark and Nicklas (1970).