BIOSYNTHETIC-STUDIES ON THE ALPHA-GLUCOSIDASE INHIBITOR ACARBOSE IN ACTINOPLANES SP - SOURCE OF THE MALTOSE UNIT

To investigate the source of the maltose unit in acarbose, feeding exp eriments using H-3- or H-2-labeled maltose or maltotriose were carried out with resting cells of Actinoplanes sp. SN223/29. It was found by experiments with [6 ''-H-3]- and [1-H-3]maltotriose that a maltose uni t from the nonreducing end of maltotriose is incorporated into acarbos e more efficiently than from the reducing end. However, experiments wi th [6 ''-H-2]- and [2-H-2]maltotriose showed that maltose from either the reducing end or from the nonreducing end of maltotriose was incorp orated into acarbose. The results established that acarbose is formed from maltotriose by two routes; (1) Sixty percent of the acarbose are formed by attachment of maltose, produced by removing a glucose exclus ively from the nonreducing end of maltotriose, to the pseudodisacchari de core unit. (2) The other 40% of the acarbose are formed by direct a ttachment of maltotriose to the core unit followed by loss of the term inal glucose from the reducing end. Furthermore, it was observed that there is no scrambling of label between the two glucose moieties of ac arbose, that maltotriose is a comparably efficient precursor of acarbo se as is maltose, and that the core unit is enriched up to 50% from th e H-2-glucose liberated from the deuterated maltotrioses.