A protective association between catalase and isocitrate lyase in peroxisomes

Glyoxysomes are specialized peroxisomes in germinating seeds, which catalyze many reactions that convert fatty acids into carbohydrates thus generating H(2)O(2). They are characterized by the presence of catalase (CAT, E.C. 1.11.1.6) in their matrix which protects cells from oxidative stress. Here, we investigated the possibility that a protein can be protected from oxidative damage by its association with CAT. We purified peroxisomal CAT from germinating castor beans by ion exchange, gel filtration, and hydroxylapatite chromatography. Gel filtration of the matrix proteins, cross-linking, and co-immunoprecipitation studies indicate that CAT associates with a glyoxysomal matrix protein, isocitrate lyase (ICL, E.C. 4.1.3.1). In addition, we found that H(2)O(2) inactivates ICL and degrades its product, glyoxylate, when CAT is inactive. ICL and its product appear to be sensitive to oxidative damage; thus, association of CAT with ICL would afford protection from H(2)O(2).