Densitograms of NADP-ICDH isoforms in peroxisomes from young (Y) and senescent (S) pea leaves. Samples of peroxisomal matrices (200 μg of protein) were subjected to IEF in a pH gradient of 3.5 to 7.0. NADP-ICDH isoforms were identified by activity staining, and gels were scanned at 560 nm. 1, ICDH-1; 2, ICDH-2; 3, ICDH-3; 4, ICDH-4.