Limited tryptic.digestion of native sucrase . isomaltase complex produced a more rapid destruction of isomaltase activity than sucrase activity. It was possible to isolate a partially fragmented sucrase subunit in high yields with a specific activity twice that of the native complex. Amino acid and carbohydrate analyses are reported and compared with the results obtained for sucrase . isomaltase complex and isomaltase subunit obtained by a different method.The sucrase . isomaltase complex from rabbit small intestine comprises a pair of digestive disaccharidases which has been localized in the brush border membrane of the enterocytes by different approaches [1,2]. The main reason for our interest in this enzymatic complex is its role in sugar translocation both in natural [3,4] and artificial lipid membranes [5]. It is a glycoprotein of approximate molecular weight 220000 consisting of two subunits, one splitting sucrose and maltose and the other isomaltose, maltose and palatinose. The existence of two active sites has been demonstrated by (a) lack of mutual inhibition between sucrose and isomaltose [6] (b) different rates of inactivation of the sucrase and isomaltase activities at pH 9.6 and 37 "C [6] and (c) differential inactivation by conduritol-B-epoxide 171.The two subunits can be separated by mild alkaline treatment [8] or by reaction with citraconic anhydride [9]. As a result of the alkaline treatment, a pure active isomaltase as well as an aggregate of inactive sucrase and a small amount of slightly active sucrase were isolated and characterized. Recently, the purification of human small-intestinal sucrase and isomaltase in small amounts together with the undissociated complex following papain treatment was reported [lo]. In the present paper we report the effect of digestion of native sucrase . isomaltase with trypsin. This process resulted in a rapid destruction of the isomaltase activity with only a slight loss of sucrase activity. As a result of this treatment it was possible to isolate in 50 % yield a Enzymes. Sucrase or sucrose z-glucosidase (EC 3.2.1.48); isomaltase or oligo-1,6-glucosidase (EC 3.2