[The metabolism of starch : II. The conversion of starch into sucrose in the cotyledons of vicia faba].

The determination of the activities of the enzymes which could be involved in the starch-sucrose conversion showed that the first step of this transfer is a phosphorolysis of starch. Both phosphorylases are able to attack the starch granules. The glu-l-P thus formed can be further metabolized to UDPG and fru-6-P, which are the substrates for the reaction catalysed by the sucrose-6-phosphate-synthetase. The activity of this enzyme increases about 4-fold during the period from immaturity to the first day of germination. The synthesis of sucrose-6-phosphate is inhibited by sucrose. This inhibition (causing an UDPG accumulation) provides a control for further starch breakdown.