Sinapine Esterase. II . Specificity and Change of Sinapine Esterase Activity During Germination of Raphanus sativus

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Abstract
Following a 20 to 24 h lag-phase after sowing, the onset of both rapid degradation of sinapine (sinapolycholine) and rapid increase in sinapine esterase activity in cotyledons of Raphanus sativus was observed. After 2 days of germination maximal enzyme activity was reached and declined in subsequent germination stages as rapidly as it had appeared. Esterases, active against indophenyl acetate, showed highest activity in dry seeds, declining to more than 50% between the 1st and 3rd day of germination. Starch gel electrophoresis showed that all protein extracts contained a multiplicity of esterases, active against α-naphthyl acetate. When gels were incubated with sinapine, one new band appeared, stainable with diazotized ρ-nitroaniline. This band represents sinapine esterase activity. Tests for substrate specificity towards cinnamic acid choline esters showed highest enzyme activity with sinapine. Studies on the occurrence of sinapine esterase in other Brassicaceae revealed that the enzyme activity coincides with the occurrence and degradation of sinapine.

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