Peroxisomes in molluscs, characterization by subcellular fractionation combined with western blotting, immunohistochemistry, and immunocytochemistry |
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Authors: | I Cancio A Völkl K Beier H D Fahimi M P Cajaraville |
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Institution: | Biologia Zelularra Atala, Zoologia eta Animali Zelulen Dinamika Saila, Euskal Herriko Unibertsitatea/Universidad del País Vasco, 644 PK, Bilbo 48080, Basque Country, Spain. |
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Abstract: | Peroxisomes of the digestive glands of mussels, Mytilus galloprovincialis Lmk, were investigated by immunoblotting and immunohistochemistry using rabbit antibodies against several mammalian hepatic
peroxisomal proteins. Western blot analysis of main subcellular fractions revealed immunoreactive polypeptides with molecular
weights comparable to those of the corresponding mammalian hepatic proteins. They could be localized to the peroxisomal matrix
in the case of catalase, multifunctional enzyme (PH), and palmitoyl-CoA oxidase (AOX), and to the peroxisomal membrane in
respect to PMP 70. The purification of peroxisomes by metrizamide density gradient centrifugation revealed the existence of
two subpopulations with densities of 1.16 and 1.20 g cm–3 exhibiting different protein compositions. In paraffin sections, positive immunolabeling for catalase was distributed along
the apical cytoplasm of the epithelia of digestive ducts and stomach and throughout the cytoplasm of digestive tubule cells.
The peroxisomal β-oxidation enzymes, AOX and PH, also appeared predominantly in the ducts and the stomach epithelia with a
weaker immunolabeling in the tubules. At the electron microscopic level a clear labeling with gold particles was observed
in the peroxisomal matrix with the anti-guinea pig catalase antibody. In addition to peroxisomes, the anti-PH antibody also
labeled the mitochondria. The similarity in the protein composition of molluscan and mammalian peroxisomes as revealed by
the present study indicates that those proteins have been well conserved in evolution suggesting that functionally peroxisomes
in molluscs could also be involved in the metabolism of lipids and in detoxification of xenobiotics. Thus, the antibodies
tested could provide useful tools for detection of peroxisomal induction in molluscan biomonitoring programs for the assessment
of aquatic environmental pollution.
Accepted: 19 October 1999 |
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