| Summary: | 碩士 === 國立中興大學 === 植物學系 === 85 === This study was aimed to investigate the biochemical properties
of NADP+-malic enzyme (malate dehydrogenase, EC 1.1.1.40) form
pineapple (Ananas comosus cv Cayenne). The NADP+-malic enzyme
extracted from detachedripening pineapple fruits was purified
31-fold after precipitating with 40﹪polyethylene glycol and
passingthrough DEAE-Sepharose and 2'',5''-ADP Sepharose columns.
Activity staining on non-denaturing polyacrylamide gels revealed
5 isozymes in the partially purified enzyme. The Km values for
L-malate and 51.7 μM, respectively.Both Mg2+ and Mn2+ were able
to serve as cofactors for NADP+-malic enzyme, with Mn2+ giving
higher activity (0.79±0.01 U/mg protein). This enzyme had a
higher pH optimum (7.5) under saturating substrate
concentration, ie., 10 mM L-malate, whereas an optimal pH of 6.5
was observed as concentration of this substrate was 0.1 mM.
Temperature optimum of NADP+-malic enzyme activity was also
analyzed, and the highest activity was detected at 70℃. After
incubation at 30, 40, 50℃ for 24hr, 66, 25 and 3﹪,
respectively, residual activity of this enzyme remained.
These results would help us design feasible protocols to bring
down extra acidity from ripening pineapple fruits and thus
improve their postharvest quality.
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