Microbody Malate Dehydrogenase Isozyme in Cotyledons of Cucumis sativus L. during Development

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Abstract
The properties of the microbody malate dehydrogenase (EC 1.1.1.37) (MDH) isozyme from cotyledons of C. sativus L. were compared during development. The isozyme remains unaltered, despite the transition from glyoxysomal to peroxisomal function that occurs during greening of the cotyledons. This conclusion is based on electrophoretic behavior, chromatographic elution from DEAE-cellulose, molecular weight, kinetic behavior and immunological identity. In most cases, the distinct properties of the other MDH isozymes in the tissue during development provide additional support for an unchanging microbody isozyme. A method for specifically assaying the microbody isozyme was developed; a diluted preparation was assayed spectrophotometrically before and after complete immunological precipitation. The turnover of the microbody MDH isozyme was investigated by a radioactive labeling study. There is incorporation into both glyoxysomal and peroxisomal MDH. Degradation rates do not correspond with decline of glyoxysomal activity or the continuation of peroxisomal activity. Apparently the microbody MDH isozyme is continually turned over throughout cotyledon development.