ISOLATION AND CHARACTERIZATION OF RAT-LIVER MITOCHONDRIAL RIBOSOMES

A procedure has been developed that allows characterization of mitocho ndrial ribosomes and quantitative analysis of the relative composition of constitutive ribosomal proteins. Purified mitochondrial ribosomes were isolated from two rat livers and shown to be active in catalyzing the polymerization of phenylalanine. They differ in sedimentation and spectral properties from cytoplasmic ribosomes isolated from the same livers. The number and relative composition of proteins present in ac tive rat liver mitochondrial ribosomes were investigated using two-dim ensional nonequilibrium pH gradient electrophoresis. There were 86 pro teins found associated with mitochondrial ribosomes in contrast to 70 proteins found associated with cytoplasmic ribosomes. Comparison of el ectrophoretic patterns revealed that cytoplasmic ribosomal proteins we re considerably more basic than their mitochondrial counterparts. Dens itometry demonstrated that the relative changes in the concentrations of these proteins can be measured quantitatively. These procedures, de veloped for use with two rat livers, allow the rat to be used as an ef ficient model for further studies into disease states of mitochondrial translation. (C) 1995 Academic Press, Inc.