The separation and characterization of liver plasma membrane fragments circulating in the blood of patients with cholestasis.

Investigations on the high molecular weight isozyme of alkaline phosphatase (R type of AP), which is typically found in the serum of patients with cholestasis, have revealed that AP of the R type corresponds to the conventional liver AP which is attached to vesicular material. The isolation of these vesicles by Sepharose gel filtration is described. Several features were found to be characteristic for these vesicles: 1. The presence of the following enzymes known to be membrane bound: alkaline phosphatase (AP), 5FEET-NUCLEOTIDASE, L-leucyl-beta-naphthylamidase (LAP), and gamma-glutamyl transpeptidase (gamma-GT). 2. The absence of the following enzymes known not to be present on cell membranes: glutamic pyruvic transaminase (SGPT), glutamic oxalacetic transaminase (SGOT), lactate dehydrogenase (LDH), and acid phosphatase. 3. The typical ultrastructural appearance and the cytochemical visualization of alkaline phosphatase and 5feet-nucleotidase. It is concluded that the vesicles correspond to fragments of the liver cell membranes that appear and continue to circulate in the blood of patients with cholestasis.