Structure-function relationships in the peroxisome: implications for human disease

Production of lactones and peroxisomal beta-oxidation in yeasts

Among aroma compounds interesting for the food industry, lactones may be produced by biotechnological means using yeasts. These microorganisms are able to synthesize lactones de novo or by biotransformation of fatty acids with higher yields. Obtained lactone concentrations are compatible with industrial production, although detailed metabolic pathways have not been completely elucidated. The biotransformation of ricinoleic acid into gamma-decalactone is taken here as an example to better understand the uptake of hydroxy fatty acids by yeasts and the different pathways of fatty acid degradation. The localization of ricinoleic acid beta-oxidation in peroxisomes is demonstrated. Then the regulation of the biotransformation is described, particularly the induction of peroxisome proliferation and peroxisomal beta-oxidation and its regulation at the genome level. The nature of the biotransformation product is then discussed (4-hydroxydecanoic acid or gamma-decalactone), because the localization and the mechanisms of the lactonization are still not properly known. Lactone production may also be limited by the degradation of this aroma compound by the yeasts which produced it. Thus, different possible ways of modification and degradation of gamma-decalactone are described.

The pathologist's approach to the diagnosis of metabolic disease

Many inborn errors of metabolism have tissue changes that suggest or indicate a diagnosis on morphologic bases. This emphasizes the involvement of the pathologist in the study of tissues obtained by biopsy as part of the diagnostic workup of cases with clinical evidence suggesting a metabolic disorder. Some of these diseases involve proteins with enzymatic activity with a consequent backlog of precursor metabolites. If these metabolites are insoluble or compartmentalized in cells, they accumulate in tissues. The diagnosis in those cases rests on establishing the nature of the accumulated materials and their topographic distribution. In some storage diseases, the abnormal substance can be identified in the affected tissues by histochemistry or ultrastructure. Another group of inborn disorders of metabolism produce changes in subcellular organelles such as peroxisomes and mitochondria. A third group is expressed by rather unique tissue changes which strongly suggest the diagnosis of metabolic disease.

Morphometry of peroxisomes and immunolocalization of peroxisomal proteins in the liver of patients with generalised peroxisomal disorders

Hepatic peroxisomes were studied by morphometric and immunocytochemical techniques in control patients and in four Zellweger syndrome patients, two infantile Refsum's (IRD) patients, one neonatal adrenoleukodystrophy (NALD) patient, and three patients with peroxisomal disorders (PD) which do not fit any currently recognised classification, but have disorders involving a defect in peroxisomal biogenesis. Peroxisomes which were ultrastructurally abnormal and greatly reduced in size and/or number were found in two of the Zellweger syndrome patients, and the NALD and IRD patients. There was variation in their numerical density ranging from none at all in two of the Zellweger syndrome patients to normal numbers in the IRD patients. In most patients there was a decrease in the immunolabelling of catalase over the peroxisomes. In the Zellweger syndrome and NALD patients, the small, abnormal peroxisomes did not label for any of the beta-oxidation proteins. The IRD patients and the PD patients however, were heterogeneous with respect to beta-oxidation labelling. The ultrastructural heterogeneity of peroxisomes in these peroxisomal disorders patients indicates there may be genotypic differences between the major groups and also within each group. The common factor in all the patients in this study where peroxisomes were present was the presence in the hepatic peroxisomes of an electron dense centre which did not label immunocytochemically for catalase or the beta-oxidation enzymes. This electron dense centre may indicate a structural abnormality in the peroxisomes in these patients.

Peroxisomal disorders in children: immunohistochemistry and neuropathology

Immunohistochemical studies with antisera against four peroxisomal enzymes, catalase and beta-oxidation enzymes (acyl-coenzyme A oxidase, bifunctional protein, and 3-ketoacyl-CoA thiolase), were performed on brain, liver, and kidney specimens from patients with peroxisomal disorders, as well as specimens from three control subjects, by using conventional paraffin-embedded autopsy material. The patients included eight with Zellweger syndrome and one with neonatal adrenoleukodystrophy. In the liver and kidney specimens from all patients, except one with Zellweger syndrome, diffuse immunostaining with all antisera in the cytoplasm of hepatocytes and renal tubular epithelium suggested an absence of peroxisomes but the presence of peroxisomal enzymes. Examination of brain specimens indicated a weak or negative reaction of neurons in the cerebral cortex and a weak reaction of glial cells in the white matter, which suggested maturational delay compared with control subjects. The delayed immunoreactive pattern of peroxisomal enzymes in Zellweger syndrome and neonatal adrenoleukodystrophy may be related to the significant neuropathologic features of polymicrogyria and dysmyelinogenesis. One patient with Zellweger syndrome had a unique finding of a positive granular catalase reaction and a negative reaction with antisera to 3-ketoacyl-coenzyme A thiolase, which suggested a diagnosis of pseudo-Zellweger syndrome. This study validates the application of these immunohistochemical methods to the study of peroxisomal enzymes. Use of these methods improves the accuracy of diagnosis of peroxisomal disorders.

An efficient screen for peroxisome-deficient mutants of Pichia pastoris

We describe a rapid and efficient screen for peroxisome-deficient (per) mutants in the yeast Pichia pastoris. The screen relies on the unusual ability of P. pastoris to grow on two carbon sources, methanol and oleic acid, both of which absolutely require peroxisomes to be metabolized. A collection of 280 methanol utilization-defective (Mut-) P. pastoris mutants was isolated, organized into 46 complementation groups, and tested for those that were also oleate-utilization defective (Out-) but still capable of growth on ethanol and glucose. Mutants in 10 groups met this phenotypic description, and 8 of these were observed by electron microscopy to be peroxisome deficient (Per-). In each per mutant, Mut-, Out-, and Per- phenotypes were tightly linked and therefore were most likely due to a mutation at a single locus. Subcellular fractionation experiments indicated that the peroxisomal marker enzyme catalase was mislocalized to the cytosol in both methanol- and oleate-induced cultures of the mutants. In contrast, alcohol oxidase, a peroxisomal methanol utilization pathway enzyme, was virtually absent from per mutant cells. The relative ease of per mutant isolation in P. pastoris, in conjunction with well-developed procedures for its molecular and genetic manipulation, makes this organism an attractive system for studies on peroxisome biogenesis.