Isoenzyme der Malat-Dehydrogenase aus Wassermelonenkeimlingen: Mikroheterogenität und deren Aufhebung bei der Samenkeimung

1) In cotyledons of dry seeds from watermelons, 10 weak bands of MDH were detectable by electrophoresis (Fig. 1). After 3 hrs of germination, this pattern was reduced to 4 stronger bands whereas the total MDH activity remained unchanged. Artifacts were excluded by use of the reverse enzyme reaction (Fig. 2), different homogenizing media and mixing experiments. 2) Molecular weight comparisons (Fig. 3) showed that with the exception of a glyoxysomal band (exclusion b Sephadex G-200) appearing at day 2 all bands and subbands had the same values (somewhat below 60000). 3) Homogenization of cotyledons from dry seeds with 10 mM β-mercaptoethanol resulted in a 4 band pattern (Fig. 8) identical to that found 3 hrs after sowing. Treatment of older cotyledons did not influence the later pattern. Electrophoresis of the raw extracts in presence of NAD or/and malate did not change the number of bands, only the R_F-values. Dialysis of raw extracts was without influence. 4) On the basis of these experiments it is concluded that during germination splitting processes of disulfide bridges take place which may result in conformation changes. According to this hypothesis dry seeds would contain 4 groups of conformational isoenzymes.