Turnover of mouse intestinal brush border membrane proteins and enzymes in organ culture. A direct evaluation from studies on the evolution of enzyme activities during the culture.

The turnover of mouse intestinal brush border membrane enzymes has been studied by kinetic analysis of the evolution of enzyme activities during organ culture. By comparing the results obtained in these studies with the predictions from a mathematical model of enzyme synthesis and degradation in organ cultures, it has been possible to reach the following conclusions: (1) There is no degradation of brush border membrane enzymes during culture and the rate of synthesis of each enzyme is directly measurable from the kinetics of total enzyme accumulation (tissue + media). (2) Brush border membrane enzymes are released in culture media by two complementary processes. The first one involves a differential solubilization of enzymes but its exact nature cannot be exactly stated. The second one involves a microvesiculation of brush border membranes, the importance of which in vivo is seen in the possible conciliation between urinary membrane synthesis and heterogeneous turnover of membrane components.