On the synthesis and incorporation of catalase and urate oxidase into the peroxisomes of mouse liver.

The processes associated with the biogenesis of peroxisomes in mouse liver have been studied by following the incorporation of radiolabelled leucine into major enzymic components of this organelle. Maximal incorporation of label into peroxisomal catalase and urate oxidase occurred within 2 hr, with the urate oxidase being labelled before catalase, but subsequent to the incorporation of phospholipid into this organelle. Subsequently, immunoprecipitation of catalase from the large granular fraction of mouse liver was shown to result in the isolation of a catalase molecule which had lost a peptide of approx. 2000 dalton from each subunit by comparison with the newly-synthesized enzyme. It was observed that the modification of catalase was obviated by the presence of leupeptin and iodoacetamide and this information has enabled the purification of both modified and unmodified forms of the enzyme. The possible significance of these data has been discussed and the major features incorporated into a working model of peroxisomal biogenesis.