Intracellular localization of malate dehydrogenase (MDH) and aspartate-aminotransferase (GOT) in seedling scutella

A study of mitochondrial and glyoxysomal isozyme mobilities is an important prerequisite for large-scale screening of enzyme genetic polymorphism by tissue homogenate analysis.

Scutella of three-day-old seedlings of Bukovinsky 3 hybrid (var. Gloria Yanetzki x inbred A344) were cut with a razor blade in the medium described by Dalling et al. (Biochim. Biophys. Acta 283:505, 1972). The slurry was filtered through three layers of cheesecloth, and the extract was layered upon a discontinuous sucrose gradient (20 - 60%), centrifuged for 4 h at 94,000xg and collected in 1 ml fractions. Cytochrome oxidase (CO) and catalase (C) served as marker enzymes of mitochondria and glyoxysomes (Fig. 1). Our zymographic data support the evidence presented by other authors that the fast-moving GOT isozyme and the slow-moving MDH isozyme are of mitochondrial origin, while the opposite is true for glyoxysomes. In contrast to the results reported by Yang and Scandalios (Biochim. Biophys. Acta 384:293, 1975), we have not found multiple forms of mitochondrial MDH. So-called "cytoplasmic" isozymes of GOT and MDH seem to be related to enzyme release from glyoxysomes during tissue homogenization.

Figure 1.

I. V. Zeleneva, L. E. Monastyreva, E. V. Savostyanova and E. E. Khavkin


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