IMMUNOLOCALIZATION OF A 43 KDA PEROXISOMAL MEMBRANE-PROTEIN IN THE LIVER OF PATIENTS WITH GENERALIZED PEROXISOMAL DISORDERS

The presence of peroxisomal membrane ghosts was examined in liver biop sies from eleven patients presenting the clinical and biochemical pict ure of a generalized peroxisomal disorder (Zellweger syndrome, neonata l adrenoleukodystrophy, infantile Refsum disease and variants of these syndromes). A polyclonal antibody raised against the membrane of huma n liver peroxisomes and recognizing a 43 kDa peroxisomal membrane prot ein (PMP) was used. In human control liver the antibodies react in a d istinct and specific way with the peroxisomal membrane. Two types of o rganelles with an immunoreactive membrane were identified in the liver parenchymal cells of the patients: organelles containing an electron- dense core and organelles with electron transparent contents. Both typ es may co-occur in the same patient; in two patients they were found i n the same cell. The organelles are rare, and their number varies betw een patients. The first type possibly corresponds to the previous morp hological description of aberrant peroxisomes in the liver of patients with Zellweger syndrome, neonatal adrenoleukodystrophy and infantile Refsum disease. The empty looking organelles have not been reported pr eviously in the liver, some of the ''empty'' organelles seem to be enc losed by a double membrane. Morphometrical analysis in three patients indicated that both types of organelles (corrected mean d-circle 0.271 -0.306 mu m for the ''empty'' and the dense core organelles, respectiv ely) are smaller than the peroxisomes in postnatal control liver and i n fetal liver. In one patient (infantile Refsum disease) immunoreactiv e organelles were not detected. The organelles with the electron-dense core were not found in two patients. In one of them, described clinic ally and biochemically as a mild Zellweger variant, very few cells sho wed numerous small organelles enclosing a morphologically normal matri x which contained at least the peroxisomal matrix proteins catalase, a cyl-CoA oxidase, 3-ketoacyl-CoA thiolase, and alanine/glyoxylate amino transferase; their membrane showed 43 kDa PMP immunoreactivity. The de nse core organelles and the empty-lookinig organelles were not found i n human control livers, in which solely the membrane of normal peroxis omes was labeled. It is therefore suggested that both types of organel les, identified by their immunoreactivity for the 43 kDa PMP, represen t aberrant peroxisomes. The finding of morphologically empty vesicles is in accordance with the concept that the defect in these disorders i s at the level of the assembly of import competent peroxisomes. On the other hand, the findings also indicate that at least in one patient t he defect is not present in all parenchymal cells: peroxisomes contain ing at least four matrix proteins mere present in a minority of the ce lls.