-Glucosidase was partially purified from Rosa 'HohJun' petals. The enzyme was highly specific for such -D-glucopyranosides as 2-phenylethyl -D-glucopyranoside. The optimal activity was observed at pH 6.0 and 35 C. The enzymes were composed with two proteins (160 and 155 kDa) by blue native-PAGE, and were classified in a family 1 glucosidase based on LC-MS/MS analyses.Key words: -glucosidase; Rosa 'Hoh-Jun'; petal; 2-phenylethyl -D-glucopyranoside; blue native-PAGE Such flower scent compounds as 2-phenylethanol (2PE), geraniol and benzylalcohol have been reported to be present in the form of monoglycosides and/or diglycosides in plant tissues.1,2) These glyco-conjugates of volatile compounds are hydrolysed by -glucosidase or endoglycosidase, e.g., -primeverosidase, to release the volatile compounds for emission from plant tissues. 3,4) In some flowers, floral scent emission is concurrent with an increase in -glucosidase activity.3) 2-Phenylethyl -D-glucopyranoside (2PE -Glc) is one of the main glycoconjugates in such Damask roses as Rosa damascena Mill. and R. 'Hoh-Jun.' 5) In our previous study, 6) we have confirmed that 2-phenyl-N-glucosylacetamidiumbromide, a glycone-specific -glucosidase inhibitor, inhibited the hydrolysis of 2PE -Glc in an enzymatic reaction by using enzymes prepared from the petals of these roses. 2-Phenyl-N-glucosyl-acetamidiumbromide also partially inhibited the emission of 2PE from rose petals. These results indicate the involvement of -glucosidase in the emission of 2PE from rose flowers. To elucidate the role of -glucosidase, we purified and characterized the enzyme from R. 'HohJun' petals.The -glucosidase activity was measured in a standard assay by the method of Yamamoto et al.7) with some modifications. The reaction mixture (200 ml) consisting of 5 mM 2PE -Glc and an enzyme solution in a 50 mM citrate buffer (pH 6.0) was incubated for 15 min at 30 C. The reaction was quenched by adding a 0.1 M trichloroacetic acid solution (100 ml). The amount of 2PE released from 2PE -Glc was analyzed by HPLC under the following conditions: column, RP-18GP Aqua (5 mm, 4:6 Â 150 mm); detection, 205 nm; column temperature, 40 C; sample temperature, 15 C; injection volume, 20 ml; mobile phase A, a 10 mM phosphate buffer (pH 6.0); mobile phase B, acetonitrile; gradient condition, 35-70% of B over 10 min; flow rate, 1 ml/ min. 2PE was detected at 3.3 min. One unit of enzyme activity is defined as the amount releasing 1 mmole of 2PE per min. The glycosidic compounds of the volatile aglycones were chemically prepared according to the reported methods. 6) Protein concentration was measured by using a DC protein assay kit (Bio-Rad), with bovine serum albumin as a standard.Cell free extracts were prepared from lyophilized R. 'Hoh-Jun' flower petals (0.5 g, stages 4 to 6) with 100 ml of buffer A (0.1 M potassium phosphate at pH 7.5, containing 0.5% 3-[(3-cholamidopropyl)-dimethylamino]-1-propanesulfonate (CHAPS), 1 mM ED-TA, 2 mM DTT, 0.5 mM PMSF, and 1% glycerol) and 1 g of Polyclar 10. After centrifuging at...