Catalysomes of adipose tissue are artefacts of enzyme localisation

Abstract

WHEN adipose tissue (insect fat body and gut, mouse mesentery) is stained to localise esterases (using 5-bromoindoxyl acetate as indigogenic substrate³) or dehydrogenases (using various substrates and nitro-blue tetrazolium⁷) the reaction product forms a single cap on each lipid droplet^8,9,11–13. The cap has been thought to be an organelle¹², perhaps a specialised mitochondrion concerned in lipid metabolism², for which Wigglesworth proposes the term catalysome. Although the localisation of the reaction products in caps is very precise, the nature of the organelle has remained a mystery. In Calpodes fat body, 5-bromoindoxyl acetate always gives one perfect blue cap of the indigo reaction product for each lipid droplet (Fig. 1a) and similar localisation is obtained with the dehydrogenases (Fig. 1b), but further studies have shown that the catalysomes are artefacts caused by the preferential precipitation of reaction products in lipid or at lipid–water interfaces.