they carry plasma membrane enzymes ( alkaline phosphatase ec 3.1.3.1 , leucine aminopeptidase ec 3.4.1.1 , 5'-nucleotidase ec 3.1.3.5 , maltase ec 3.2.1.20 ) in the same ratio as the membranes of the cells of origin .
C0002059
alkaline phosphatase
C0020289
ec 3