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The main polypeptide isolated from lens fiber membrane has been solubilized in octyl glucoside and studied by gel filtration in high-performance liquid chromatography (HPLC). The combination of S 20,wvalue obtained from analytical ultracentrifugation and Stokes radius determined by HPLC of the soluble fraction indicates that more than 90% of the protein is monomeric. The solubilization of the protein seems to be dependent upon the presence of the NH 2and COOH terminal sequences, since proteolytic degradation of MP26 which removes these terminal sequences is less soluble than the uncleaved polypeptide. Moreover, there is a higher amount of oligomer after proteolysis. Fatty acid analysis by gas chromatography shows that the insoluble membrane fraction from both cortical and nuclear fibers comprises a special class of long (C22) saturated fatty acids (behenic acid).

The structural properties of the cell envelopes of Mycobacterium leprae and Mycobacterium lepraemurium were investigated by freeze-fracture, freeze-etching, and negative-staining techniques. Freeze-fracture split the cell wall and exposed the internal features of the peptidoglycolipid mycosidic filamentous network. The cell membrane was also split into two asymmetric faces. The external fracture face was characterized by linear arrays of intramembranous particles, whereas the protoplasmic fracture face showed randomly distributed clusters of particulate entities. Comparative analysis of the ultrastructural features observed in M. leprae and M. lepraemurium indicated that the organization of the cell envelope in these two species differed particularly with respect to the amount and complexity of the superficial peptidoglycolipid and mycosidic integument, which is poorly developed in the mycobacterium responsible for human disease.

The correlation between gap junction morphology and the state of electrical coupling was investigated in the frog auricle, which presents an atypical gap-junction organization. Electrical uncoupling of the tissue was achieved by perfusion with CO2 -saturated Ringer medium. The tissue was fixed with glutaraldehyde and freeze-fractured before and during the application of CO2 -saturated Ringer medium and after returning to the initial medium. The electrical tissue coupling was assayed by microelectrode recording just before fixation. At least 97% uncoupling was induced by CO2 -saturated Ringer medium, as estimated from double sucrose gap experiments on several single atrial trabeculae. Several modifications were induced by CO2 -saturated Ringer medium. A decrease in the number of particles per junctional assembly and dispersion of these assemblies in the plane of the membrane, indicate a decrease in the organization of the gap junctions. In parallel, loose clusters of particles became evident on the P-fracture face of the membrane. The size of the particles in these clusters was larger than the size of the background particles, and of the gap junction particles. They never corresponded with complementary pits on the E-fracture face. On return to the initial Ringer perfusion medium the cell coupling was reversed and the gap junction dispersion was also reversed. However, the gap junctions remained small. The relationship between these morphological modifications and the conducting state of the tissue is discussed.