Properties of ATPase activity associated with peroxisomes of rat and bovine liver.

1. Peroxisomes were isolated from bovine and rat liver by use of differential and density gradient centrifugations. 2. In the final density gradient (Nycodenz) a distinct peak of ATPase activity codistributed with the peroxisome marker catalase and was well separated from the bulk of the ATPase activity and from markers for other subcellular organelles. 3. The peroxisome-associated ATPase had a pH optimum of 7.5 and was inhibited by N-ethylmaleimide, by N,N'-dicyclohexylcarbodiimide and by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole, but was unaffected by up to 30 microM n-tributyltin chloride. 4. Prolonged incubation with oligomycin at high concentrations indicated that 50% of peroxisomal ATPase was resistant to this inhibitor. The oligomycin-sensitive ATPase activity required at least a four-fold higher ratio of inhibitor to protein for inhibition than mitochondrial ATPase did. It was concluded that oligomycin-sensitive and oligomycin-resistant ATPase may be associated with liver peroxisomes.     

Protein synthesis by brain-cortex mitochondria. Characterization of a 55S mitochondrial ribosome as the functional unit in protein synthesis by cortex mitochondria and its distinction from a contaminant cytoplasmic protein-synthesizing system

Homogenates of rat brain cortex were fractionated by conventional methods of velocity sedimentation and separated into a microsomal and a washed mitochondrial fraction. By electron microscopy the mitochondrial fraction was shown to be rich in synaptosomes. The mitochondria-synaptosome fraction synthesized protein in vitro by a route that was partially inhibited by cycloheximide and partly by chloramphenicol. The relative effectiveness of the two inhibitors varied greatly with the medium used. In the mitochondria-synaptosome fraction active 80S cytoplasmic ribosomes and active 55S mitochondrial ribosomes were detected; these were also seen in the electron microscope. Mild osmotic shock of the mitochondria-synaptosome fraction followed by velocity sedimentation in sucrose-EDTA allowed isolation of a mitochondrial fraction free of synaptosomes. Protein synthesis in this fraction was entirely inhibited by chloramphenicol, but was completely resistant to cycloheximide both in a medium promoting oxidative phosphorylation and in ATP-generating medium. Ouabain had no inhibitory effect on protein synthesis in a purified mitochondrial preparation. It is concluded that brain-cortex mitochondria synthesize protein entirely on 55S mitochondrial ribosomes.     

Subcellular fractionation evidence for a putative peroxisome-mitochondrion attachment in the liver of normal and genetically obese (ob/ob and db/db) mice.

1. Liver post-nuclear supernatants (PNS) from several mouse strains were fractionated by zonal centrifugation and fractions analysed by marker-enzyme estimations+electron microscopy. 2. Rate-dependent banding of PNS yielded peroxisome-enriched (PER) and mitochondrion-enriched (MER) regions. 3. Density-dependent banding of PER yielded peroxisomes (approximately 1.22 g/ml) well separated from mitochondria (approximately 1.8 g/ml). 4. Density-dependent banding of MER yielded peroxisomes that co-distributed with mitochondria and electron microscopy revealed close proximity of the two organelles. 5. Experiments demonstrated that co-distribution was not due to weak binding of proteins or to agglutination of organelles. 6. The results indicate in vivo attachment of some mitochondria and peroxisomes.     

A Three-dimensional model reconstruction of pole assembly in Bacillus subtilis

In the rod-shaped bacterium Bacillus subtilis, new polar surfaces arise at division through the centripetal synthesis of a centrally located cross-wall. Subsequently, the cross-wall, analogous to a flat annulus, is converted into two inner layers of polar wall as the daughter cells separate. The junction of polar and cylindrical wall is marked by the presence of raised tears or wall bands formed by the splitting apart of the cross-wall at its base. New polar wall formed in this manner accounts for about 15% of the total surface area. The sequence of pole formation has been simulated by means of a generalized conic section based upon the mathematical rotation of a parabola about its longitudinal axis. Four basic measurements describe the stages of pole formation with reference to polar surface area: the equatorial diameter at the wall bands (D_max), the division furrow (D_min), the horizontal distance (h) from the centre of the cross-wall to D_max and the curvature of the nascent polar surfaces. These four parameters were found to yield a close fit to measurements of polar size and shape derived from electron micrographs of cell poles in sectioned organisms. Calculations of pole curvature suggest that both the initial separation of the cross-wall and separation of the daughter cells may occur very rapidly.