Protein disulfide isomerase (PDI E.C. 126.96.36.199) catalyses the formation of disulfide bonds in secretory or cell-surface proteins during their biosynthesis. PDI activity is associated with the microsomal fraction of the cell and has been found in several mammalian tissues and in developing wheat endosperm.
The embryo and aleurone layer of germinating seeds of the wheat cultivar Galahad showed PDI activity associated with a microsome-enriched fraction of cell homogenates PDI activity in microsome-enriched fractions from aleurone layers of normally germinating seeds was significantly higher than in their abnormally germinating counterparts and diminished as germination proceeded.
Dry embryos and germinating embryos showed less PDI activity than aleurone layers. There was no significant difference in PDI activity between microsome-enriched fractions from embryos of normally and abnormally germinating seeds at 3 or 6 days of germination.
Wheat aleurone PDI was partially purified using gel filtration and had a molecular mass of 110–130 kDa and a monomeric molecular mass of ca. 57 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis.