The loss of enzyme reaction products from ultrathin sections during the staining for electron microscopy

Problems with ultrastructural demonstration of aryl sulphatase activity in rat liver parenchymal cells

The classical method for the electron microscopical demonstration of aryl sulphatase activity in lysosomes (Hopsu-Havu et al. 1967) has been applied for selective demonstration of lysosomes in rat liver parenchymal cells. A positive reaction was obtained in some lysosomes, but the greater part of the precipitate was found in the form of big conglomerates which frequently filled up the interstices between various organelles rather than that they were localized within the organelles. Modifications of the procedure in order to try to confine the demonstration of enzyme activity to lysosomes only included measures: To reduce the amount of primary reaction product, to improve the trapping efficiency of the incubation medium, to prevent possible displacement of the final reaction product. Extralysosomal precipitate persisted under all circumstances; this is interpreted as an artefact rather than as a demonstration of enzyme activity localized in vivo in the cytoplasmic matrix. It is concluded that the present method for demonstration of aryl sulphatase activity is not well suited for microscopical identification of lysosomes in rat liver parenchymal cells.

Osmiophilic reagents in electronmicroscopic histocytochemistry

Direct histocytochemical staining methods on undisrupted tissues, stabilized by chemical fixation, potentially offer perhaps the most reliable approach to the study of the enzymes of the cell with relation to its ultrastructure. The atoms which, for the most part, comprise the biomacromolecules and enzymes of cells and tissues contribute little to their inherent electron opacity or ability to scatter electrons differentially. The latter property of a substance is responsible for its observation with the electron microscope. Since the introduction of osmiophilic reagents into cytochemistry (HANKER et al. 1964), the selective deposition of relatively large amounts of polymeric osmium black reaction products at the subcellular sites of insoluble or immobilized enzymes or biomacromolecules has facilitated their demonstration with the light and electron microscopes. Perhaps the most widely employed osmiophilic reagent in histocytochemistry has been DAB which was introduced by GRAHAM and KARNOVSKY (1966a, b). Although it receives its widest use for demonstrating the sites to which the exogenous ultrastructural tracer horseradish peroxidase (HRP) is transported in vertebrate tissues, it is also widely employed for the demonstration of catalase in peroxisomes with the media of FAHIMI (1969) or of NOVIKOFF and GOLDFISCHER (1969), and for the demonstration of cytochrome oxidase with the medium of SELIGMAN et al. (1968a). The importance of this reagent lies in its ability to undergo oxidative polymerization forming an insoluble osmiophilic melanin-like product (HANKER et al. 1972a) which comforms well to ultrastructure, at the sites of enzymic or nonenzyme proteins which catalyze its oxidation. In the past few years, studies in our laboratory have shown that a rational approach to the histocytochemical demonstration of enzymes could be devised. It is based on the selective deposition of transition metal compounds at the sites of enzymes that resemble hemoproteins in their ability to catalyze the oxidative polymerization of DAB. The most useful of these compounds, cupric ferrocyanide (Hatchett's brown) was also introduced into cytochemistry by Karnovsky's laboratory (KARNOVSKY 1964; KARNOVSKY and ROOTS 1974). By the use of natural substrates, when available, or synthetic substrates which liberate or form a reducing agent at the sites of the enzymatic activity, many diverse types of enzymes have been demonstrated by methods depending on this principle known as catalytic osmiophilic polymer generation. DAB has probably been the most useful histocytochemical reagent of the past decade. Yet its borderline carcinogenicity and the frequent interruption of a supply of good quality DAB have encouraged research into a substitute reagent. A new substitute for DAB has resulted from the study of artificial melanins in our laboratory for several years. It consists of a mixture of p-phenylenediamine and pyrocatechol and is much better than DAB for the demonstration of HRP used as a cytochemical tracer...

The demonstration of arylsulfatases with 4-nitro-1,2-benzenediol mono(hydrogen sulfate) by the formation of osmium blacks at the sites of copper capture

A new method is described for the direct cytochemical demonstration of lysosomal arylsulfatases utilizing a synthetic substrate, 4-nitro-1,2-benzenediol mono(hydrogen sulfate), and a copper capture reaction. A small amount of Hatchett's brown (cupric ferrocyanide, Cu2Fe(CN)6-7 H2O) formed at the subcellular sites of copper capture is then utilized as a heterogeneous catalyst to effect the oxidative polymerization of 3,3'-diaminobenzidine which results in the formation of an insoluble, highly colored osmiophilic indamine polymer at the sites of enzymatic activity. The reaction product even at this stage prior to osmication is highly visible. It is readily seen with a light microscope in 50 mum sections of fixed tissues prepared with a mechanical chopper or in 10 micron cryostat sections treated for arylsulfatase activity. Upon osmication, an electron-opaque osmium black is formed which is much less soluble than the products of either the lead or barium capture reactions currently used for the demonstration of arylsulfatase with the electron microscope. The selection of areas of plastic-embedded tissues for ultrathin sectioning is facilitated by the ready visibility of these osmium black end products on 1-2 mum plastic sections which can be studied with the light microscope. This method gives permanent specimens demonstrating arylsulfatases A or B in lysosomes and autophagic vacuoles. In addition, enzyme activity is seen occasionally in the Golgi region or lamellae of certain cells believed to be elaborating sulfated products. In these instances, it may be demonstrating sulfotransferase activity.

Uranium localization on hydroxyapatite by analysis of fission fragment tracks

The distribution of enriched uranium on individual hydroxyapatite crystals after an exchange reaction has been investigated by means of thermal neutron irradiation followed by electron microscopic analysis of fission fragment tracks in plastic support films. One uranyl ion for every two to three surface calcium ions became associated with the mineral but in a nonuniform distribution that strongly favors crystal end regions.