GRAPE (VITIS-VINIFERA L) MALATE-DEHYDROGENASE - PARTIAL-PURIFICATION AND ISOELECTRIC HETEROGENEITY

Using ion-exchange chromatography and isoelectric focusing in a liquid medium, it was shown that malate dehydrogenase exhibited a high molecular heterogeneity in grape as in most living organisms. Two groups of isozymes with very close molecular weights (80 000 0) were separated on the basis of their net electric charge at pH 7.6 into an acidic protein group (pl 4.0 to 5.5) and a less acidic protein group (pl 5.5 to 7.5). Two main acidic proteins (pl close to 4.9 and 5.2) seem to be always present whatever the cultivar while the presence of less acidic subforms appeared to be more fluctuating. The enzyme molecular heterogeneity observed for berries was also found on other vine tissues : thus, isozymes of in vitro cultivated cells were mainly constituted by acidic subforms, whereas, in the leaves, they were present in two basic subforms (pl 8.4 and 9.0).