| Abstract: | The luminal plasma membrane of calf urinary bladder epithelium (urothelium) has been isolated by a method designed to preserve enzymic activity as well as structural integrity. The yield was about 80 micrograms per calf bladder. Low levels of 5' nucleotidase, Mg2+-ATPase and (Na+ + K+)-ATPase activities were found in the luminal membrane fraction. Cerebroside was the major lipid present and dodecyl sulphate gel electrophoresis revealed a complex protein and glycoprotein composition in the whole membrane. A membrane fraction consisting of only the plaque areas was shown to have a simpler protein composition with major polypeptides of apparent Mr 12 000 and 22 000. These may associate to form a 30 000 apparent Mr complex which could represent the individual 'particles' of the dodecameric subunits seen by electron microscopy in the plaque regions. |
