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A variety of plant species have been shown to catalyse anomeric acyl exchange from a number of 1- O -fatty-acyl-β-glucoses as donor substrates to [ 14 C]-glucose as an acceptor. The activity in wild tomato Lycopersicon pennellii has been analysed in detail by using analogs of glucose as acceptors and a number of 1- O -acyl-β-glucoses and 1- O -acyl-2-deoxyglucoses as acyl donors. Compared to 1- O -isobutyryl-β-glucose, the analogous 1- O -isobutyryl-β-2-deoxyglucose is an effective donor both to glucose (ca. 75%) and to 2-deoxyglucose (ca. 95%). On the contrary, compared to 1- O -isobutyryl-β-glucose, 1- O -isobutyryl-α-2-deoxyglucose is a poor donor both to glucose (ca. 4%) and to deoxyglucose (ca. 6%). The glucose analogs free at the anomeric center such as 3- O -methylglucose and 2-deoxyglucose are competent acyl acceptors from various 1- O -acyl-β-glucoses whereas 1- O -methylglucose is not. The primary initial product of acyl transfer from 1- O -isobutyryl-β-glucose to [ 14 C]-glucose is β-glucosidase-cleavable 1- O -acyl-[ 14 C]-β-glucose, whereas the isobutyryl-[ 14 C]-3- O -methylglucose generated from 1- O -isobutyryl-β-glucose and [ 14 C]-3- O -methylglucose is β-glucosidase-resistant. The transfer of the acyl group to 3- O -methylglucose occurs at the anomeric center; therefore the resistance to β-glucosidase reflects the strict specificity of β-glucosidase for glucose. |
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