468 SUGAR HYDROLASES OF THE INFANT RAT INTESTINE AND THEIR ARRANGEMENT ON THE BRUSH BORDER MEMBRANE

The brush border membrane of the immature rat intestine contains lactase and maltase as the predominant sugar hydrolases, through the suckling period of the animal. These enzymes were isolated in high purity (lactase S.A. 23, maltase S.A. 58) from infant rat intestine and monospecific antisera (rabbit) were prepared to each. Brush border membranes from 15-day old rats were isolated in excess of 25-fold purification (using lactase as a membrane marker enzyme) by procedures yielding membranes at 2 to 3-fold greater purity from infant rat intestine than reported previously (Galand and Forstner, Biochem.J.(1974)144:293).Incubation of brush border membranes with anti-maltase and anti-lactase resulted in binding of each antibody in stoichiometric equivalence to that obtained with the respective pure enzyme. Thus, it could be concluded that each of the sugar hydrolases exist on the membrane fully exposed and equally available to antibody as is the free enzyme in solution. Furthermore, the binding of antibody to one did not affect the immuno-titration curve of the other nor its extractability by papain or Triton X-100. Each of the sugar hydrolases, therefore, is a brush border membrane surface component, which is independently placed in relation to the other and arranged so that its unique antigenic determinants are fully available for immunoreactivity.(Supported by N.I.H. grants HD-49, HD-02147, HD-00391, CA-14917.)