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Metabolism and Enzymology

Partial Characterization and Subcellular Localization of Three -Glucosidase Isoforms in Pea (Pisum sativum L.) Seedlings ¹

Department of Agronomy, University of Wisconsin, Madison, Wisconsin 53706-1597, Cereal Crops Research Unit, U.S. Department of Agriculture, Agricultural Research Service, University of Wisconsin, Madison, Wisconsin 53706, Department of Agronomy, University of Wisconsin, Madison, Wisconsin 53706

Three isoforms of -glucosidase (EC 3.2.1.20) have been extracted from pea (Pisum sativum L.) seedlings and separated by DEAE-cellulose and CM-Sepharose chromatography. Two -glucosidase isoforms (G1 and G2) were most active under acid conditions, and appeared to be apoplastic. A neutral form (G3) was most active near pH 7, and was identified as a chloroplastic enzyme. Together, the activity of G1 and G2 in apoplastic preparations accounted for 21% of the total acid -glucosidase activity recovered from pea stems. The vast majority (86%) of the apoplastic acid -glucosidase activity was due to G1. The apparent K_m values for maltose of G1 and G2 were 0.3 and 1.3 millimolar, respectively. The apparent K_m for maltose of G3 was 33 millimolar. The respective native molecular weights of G1, G2, and G3 were 125,000, 150,000, and 110,000.

¹ This material is based upon work supported by the Cooperative State Research Service, U.S. Department of Agriculture (USDA) under agreement No. 87-CRCR-1-2324, by the College of Agriculture and Life Sciences, University of Wisconsin-Madison, and the USDA-Agricultural Research Service.

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