Ultrastructural localization of enzymes

In situ staining of activities of enzymes involved in carbohydrate metabolism in plant tissues

A powerful technique is described to localize the activities of a range of enzymes in a wide variety of plant tissues. The method is based on the coupling of the enzymatic reaction to the reduction of NAD and subsequent reduction and precipitation of nitroblue tetrazolium. Enzymes that did not reduce NAD could be visualized by coupling their activities to glucose-6-phosphate dehydrogenase activity via one or more intermediary 'coupling' enzymes. The method is shown to be applicable for the detection of the activities of hexokinase, fructokinase, sucrose synthase, uridine 5'-diphospho-glucose pyrophosphorylase, ADP-glucose pyrophosphorylase, phosphoglucomutase, and phosphoglucose isomerase. It could be used for all tissues tested, including green leaves, stems, roots, fruits, and seeds. The method is specific, very sensitive, and has a high spatial resolution, giving information at the cellular and the subcellular level. The localization of sucrose synthase, invertase, and uridine 5'-diphospho-glucose pyrophosphorylase in transgenic potato plants, carrying a cytokinin biosynthesis gene, is studied and compared with wild-type plants.

Ethanolic dehydration and its effect on membrane-bound enzymes of Chlorogloeopsis fritschii and Chlorella pyrenoidosa

Ethanolic dehydration (20% to 70%) of the thylakoid membranes of Chlorogloeopsis fritschii resulted in an 8% to 58% loss of glutamine synthetase activity. In Chlorella pyrenoidosa, hydroxypyruvate reductase and fumarase, marker enzymes of the peroxisomes and mitochondria, respectively, diffused from the organelles on dehydration.

Electron microscopy of undecalcified human bone

An alternative approach for the electron microscopical examination of undecalcified human bone was investigated. The method required bone to be chilled to -70 degrees C, sectioned at 10 microns in a special bone cryostat, and these sections to be fixed and embedded for ultrathin sectioning. Good preservation of bone cells was seen. The advantages of this method are that it allows numerous particular regions of the 10 microns thick sections to be selected under normal light microscopy, and these regions to be then selected for electron microscopy. The 10 microns sections allow for excellent penetration of the fixative and thus better preservation of the tissue is more likely.

Differential localization of alkaline phosphatase in barrier tissues of the frog and rat nervous systems: a cytochemical and biochemical study

We investigated the localization of alkaline phosphatase (AP) in the peripheral and central nervous systems of the frog (Rana pipiens) and rat. In the frog sciatic nerve, AP reaction product was seen as a precipitate within caveolae and vesicular profiles of perineurial cells, and frequently filled the extracellular space. In the rat peripheral nerve, AP reaction product appeared as small tufts on the cell surfaces and within vesicular profiles of endoneurial blood vessels. AP reaction product was not detected in the rat perineurium or in endoneurial blood vessels of the frog. In the frog central nervous system, AP reaction product was detected in the arachnoid membrane adjacent to the subarachnoid space, but not in the cerebral or pial vessels, whereas in the rat it was detected in the outer arachnoid membrane and in the cerebral and pial blood vessels. Biochemical analysis indicated a sevenfold higher AP activity in the frog perineurium over the endoneurium, whereas in the rat, threefold more activity was measured in the endoneurium over the perineurium. Levamisole, an AP inhibitor, decreased the enzyme activity by 95% in rat tissues, and by 70% in frog tissues and in plasma from both animals. Similar decrements were observed cytochemically. This study suggests that: (1) the distribution of AP varies between species, but that it is always present in at least one component of the blood-brain and blood-nerve barriers, (2) because barrier tissues of the nervous system have enzymatic activity, they may biochemically modify the adjacent environment, (3) vesicular profiles and caveolae in the blood vessels and perineurium may function as microenvironments for enzymatic activity, and (4) in the rat and frog, different isozymes of AP may be present.

Endocytic pathways and time sequence of lysosomal transfer of macromolecules in cultured mouse peritoneal macrophages. Double-labeling experiments with horseradish peroxidase and ferritin

A double-labeling protocol was used to study endocytic pathways and lysosomal transfer of exogenous macromolecules in cultured mouse peritoneal macrophages. After pulse-chase labeling of lysosomes with horseradish peroxidase (visualized cytochemically), the cells were exposed to native, anionic ferritin for 0-45 min at 37 degrees C and then analysed by transmission electron microscopy. The results show that ferritin binds to the plasma membrane, accumulates in coated pits, and is rapidly taken up in small, smooth-surfaced endocytic vesicles. The latter carry the ferritin molecules directly to lysosomes, recognized by their peroxidase labeling, or fuse with each other to form larger endocytic vacuoles (endosomes) which in turn fuse with and empty their content into lysosomes. The first signs of transfer of ferritin into the lysosomes were seen after 5-10 min of exposure and after 25-30 min most of the lysosomes were labeled. Union of ferritin-labeled and other lysosomes was also noted, suggesting that the contents of the lysosomes were spread within the lysosomal compartment by fusion-fission processes. It is concluded that a multiplicity of structures is involved in the uptake and intracellular transport of exogenous macromolecules in macrophages and that the time sequence of lysosomal transfer of the interiorized material is highly variable.

Compartmentation of glycolytic and glycogenolytic metabolism in vascular smooth muscle

Vascular smooth muscle is characterized by a high rate of aerobic lactate production, which may be altered independently of oxidative phosphorylation. This finding suggested a cytoplasmic compartmentation of metabolism. Exogenous glucose was found to be the sole precursor of aerobic glycolysis under unstimulated conditions. Although tissue depolarization with high K+ resulted in a substantial reduction of endogenous glycogen, exogenous glucose remained the sole precursor of aerobic lactate production. These data showed unequivocally that carbohydrate metabolism is compartmentalized in vascular smooth muscle.

Electron-microscopic identification of Gomori-positive rings in normal spinal cord white matter

Longitudinal vibratome slices from glutaraldehyde-fixed adult guinea pig lateral funiculus white matter were incubated in a Gomori medium, stained with ammonium sulfide, osmicated and section-embedded in vestopal. Following light-microscopic localization of ring-shaped deposits of reaction product series of thin sections were cut from these areas. In the electron microscope ring-shaped deposits of reaction product were consistently found to surround lamellated myelinoid bodies within glial cells. By following the series some of these cells could be identified as microglia. Sparse aggregates of reaction product were occasionally seen outside myelinoid bodies in typical astrocytes. Precipitates were not related to myelinoid bodies associated with typical oligodendrocytes. The findings suggest that microglia and possibly astroglia participate in the breakdown of spontaneously formed myelin fragments in normal adult white matter.

An ultrastructural study of vascular proliferation and vascular alkaline phosphatase activity in the developing cerebral cortex of the rat

Alkaline phosphatase cytochemistry was employed to study the distribution of this enzyme in blood vessels during vascular differentiation and maturation during the postnatal development of the rat cerebral cortex. Enzyme reaction product was present in early vascular sprouts, and also throughout the subsequent maturation and differentiation of capillaries and arterial vessels. Cerebral capillaries appeared to be patent soon after the fusion of a sprout tip with another vessel; no evidence for delayed or synchronous opening was obtained. The distribution of alkaline phosphatase reaction product in vessel walls changed during vascular maturation. In vascular sprouts, reaction product was found mainly in the narrow lumen. As vessels became patent, reaction product appeared also on abluminal surfaces, at first chiefly in the narrow spaces between overlapping vascular cells. As vessels matured, reaction product became more generally distributed around the abluminal surface. In relatively mature capillaries and arterial vessels, it was restricted largely to endothelial cell surfaces and the spaces between smooth muscle cells. The significance of this distribution is unknown. Some possible explanations, including the possibility of artifact, are discussed. No alkaline phosphatase reaction product was found in differentiated veins.

Redistribution of membrane proteins in isolated mouse intestinal epithelial cells

Single mouse intestinal epithelial cells (IEC) may be isolated by the use of a combination of methods used for the isolation of IEC from other species. Isolated cells remain viable for several hours. The membrane integral enzymes alkaline phosphatase and leucine aminopeptidase of isolated IEC are localized to the brush borders of IEC in tissue and in most newly isolated IEC. With time, both enzymes are found distributed over the entire cell surface. Redistribution appears to occur by diffusion in the plane of the membrane. It is slowed, but not blocked, if cells are maintained at 0 degrees C instead of at 37 degrees C, and it is not blocked by fixation in 0.5-3% paraformaldehyde. Drugs that alter cell membrane potential or that affect cell levels of ATP enhance the rate of redistribution of the enzymes.

Evidence that insulin causes translocation of glucose transport activity to the plasma membrane from an intracellular storage site

The glucose transport activity of fat cells was assayed in a cell-free system. The activity was solubilized and incorporated into egg-lecithin liposomes. The carrier-mediated glucose transport activity was estimated by subtracting the cytochalasin B-insensitive component from the total glucose uptake activity of the modified liposomes. When a crude microsomal preparation from fat cells was fractionated by sucrose density gradient centrifugation, two transport activities (peaks A and B) were separated. Peak A coincided with the peak of 5'-nucleotidase, a marker of the plasma membrane. Peak B appeared to coincide with the peak of UDPGal:N-acetylglucosamine galactosyltransferase, a marker of the Golgi apparatus. Peak A was considerably smaller than peak B under basal conditions. When cells were exposed to 1 nM insulin for 5 min before homogenization, the height of peak A increased whereas that of peak B decreased. Insulin had no significant effect on the galactosyltransferase activity. The Km values of glucose transport facilitated by the activities in peaks A and B were both approximately 10-15 mM. These results imply that insulin facilitates translocation of the transport activity from an intracellular storage site to the plasma membrane.

The dynamics of membrane structure

The membranes of living organisms are involved in many aspects of the life, growth and development of all cells. The predominant structural elements of these membranes are lipids and proteins and the basic strucvture of these molecules has been reviewed. The physical properties of the lipid constituents particularly their behavior in aqueous systems has led to the concepts of thermotropic and lyotropic mesomorphism; the interaction between different types of lipid molecules modulate this behavior. Interaction of phospholipids in aqueous systems with cholesterol, ions and drugs have been examined in this context. In addition a variety of model lipid-protein systems have been investigated and the implications of interactions between lipids and different proteins in biological membranes has been evaluated. This leads to a detailed consideration of the way lipids and proteins ae organized in cell membranes and contains an appraisal of the evidence supporting contemporary views of membrane structure. Particular attention has been devoted to the question of how mobile the components are within the structure. Particular attention has been devoted to the question of how mobile the components are within the structure. Finally the biosynthesis, turnover and modulation of the properties of interacting membrane constituents is critically reviewed and possible ways of controlling the behavior of cells and organisms by altering the structural parameters of different membranes has been considered.

Adenylate cyclase cytochemistry: a methodological evaluation

A cytochemical method for the demonstration of adenylate cyclase activity has been evaluated. Enzyme activity in the epithelium of the Müllerian part of the vaginal anlage in neonatal, oestradiol-treated mice has been studied under different experimental conditions. The effects of fixation, incubation conditions and post-fixation have been studied. Variations in the amount of impurities and acid content of the glutaraldehyde do not seem to influence the enzyme activity. High Pb2+ ion concentration seems to promote unspecific staining. Under standard conditions [2 mM Pb (NO3)2' pH 7.2, and incubation temperature 30 degrees C], neither non-enzymatic nor nonsubstrate-dependent lead trapping in the tissue could be observed. The possible contribution of other enzymes utilizing ATP and AMP-P(NH)P as the formation precipitate, has been evaluated. Both ATP and AMP-P(NH)P have been used as substrates in this study. Provided the appropriate control experiments are performed, this cytochemical method is reliable for demonstration of adenylate cyclase activity.

Ultrastructural demonstration of dehydrogenases in rat cerebral cortex

Techniques for the ultrastructural demonstration of dehydrogenases in cerebral cortex are described. The best fixation for good fine structural preservation and retention of LDH and NADH-diphorase was obtained by perfusion with a misture of formaldehyde and glutaraldehyde and for SDH by perfusion with formaldehyde. Comparison of incubation conditions showed that consistent results were obtained using enzyme markers NBT and DS-NBT for LDH and NADH-diaphorase: DS-NBT was more satisfactory than NBT and BSPT for SDH. Penetration of incubation media was improved by Triton X-100: DMSO and ultrasonic treatment were less effective. The techniques enabled the first electron cytochemical demonstration of dehydrogenases in different elements of prefixed cerebral cortex. Ultrastructural sites of enzyme activities were localized within cristae and inter-membrane spaces of mitochondria in nerve cell cytoplasm and its processes, oligodendrocytes and astrocytes. Authenticity of the ultrastructural sites was confirmed by four different control experiments.

Electron microscope histochemical localization of alkaline phosphatase(s) in Bacillus licheniformis

Sites of alkaline phosphatase (APase) activity in a facultative thermophilic strain of Bacillus licheniformis MC14 have been localized by electron microscope histochemistry, using a lead capture method. The effects of 3% glutaraldehyde and 3.0 mM lead on APase activity were investigated, and these compounds were found to significantly inhibit enzyme activity, 68 and 18%, respectively. A number of parameters were varied in studies to localize APase activity, including: growth temperature (55 and 37 degrees C); substrate concentration in the histochemical mixture (0.06, 0.15, 0.30, 1.00 mM); fixatives; protoplast preparations and whole cells; phosphate-repressed and -derepressed cells; and age of vegetative cells (mid-log and late log). These variations affected the number but not the location of lead phosphate deposits, which appeared at discrete sites along the inner side of the cytoplasmic membrane. Control cells incubated in histochemical mixtures lacking substrate, lead, or both exhibited no lead phosphate depositis. The histochemical localization at membrane sites correlated well with biochemical localization data, which indicated that greater than 80% of the APase activity was associated with the membrane fraction in logarithmically growing cells.

Remarkable electron-microscopic localization of thiamine diphosphate phosphohydrolase (TDPase) in the tanycytes of the rat

The electron-microscopic localization of TDPase in the tanycytes of rat brain was studied. The reaction product was demonstrated in the membranes, but not in the Golgi apparatus of this cell type. Possible functional aspects of these findings were discussed.

Enzyme histochemistry as a link between biochemistry and morphology

The presented paper describes the role of enzyme histochemistry in cell biological investigations. In the first chapter a general discussion has been given about enzyme histochemistry as a connecting link between biochemistry and morphology. The methods available for determination of enzymes in a particular cell or cell compartment have been reviewed. In this respect the characteristics of enzyme histochemistry have been discussed. Furthermore, attention has been paid to the possibilities and limitations of enzyme histochemistry. In chapter two a comparison has been made between histochemically judged and biochemically determined enzyme activities. Some fundamental differences between the biochemical and the histochemical approach in cell biological investigations are dealt with. To correlate histochemically and biochemically determined enzyme activities, a description has been given of the application of histochemical methods on isolated fractions and sucrose-ficoll gradients of these fractions. Several experimental results are described concerning the question whether a relation exists between histochemically and biochemically determined activities of respectively alkaline phosphatase, glucose-6-phosphatase, 5'-nucleotidase and 3ss-hydroxysteroid dehydrogenase. From these results the conclusion could be drawn that in general a good correlation exists between histochemically judged activity per volume (area X thickness) and biochemically determined activity per gram tissue. In chapter three the role of enzymes as markers of cellular particles and as parameters of metabolic pathways is described. Histochemical methods are available for most marker enzymes. Only activities of key enzymes can be regarded as parameters of metabolic pathways. The distribution in sucrose-ficoll gradients of enzymes, regarded as markers of mitochondria, lysosomes, endoplasmic reticulum and plasma membranes has been given. The changes occur ing under different experimental conditions for a number of marker enzymes in rat liver are described. Attention has been given to the contibution of enzyme histochemistry in the study of the heterogeneity of mitochondria, the dual localization of some (lysosomal) enzymes, the complexity of the microsomal fraction, the function of the Golgi apparatus and the heterogeneity and function of plasma membranes. Based on these results and on literature findings the possible role of some marker enzymes in cell metabolism has been discussed. In chapter four problems coherent with species and sex differences in enzyme activities are described. The interpretation of histochemical and biochemical results in view of these differences is discussed. Enzymes characteristic for a given cell type -3ss-hydroxysteroid dehydrogenase in steroid producing cells, ATP-ase in liver plasma membrane surrounding the bile canaliculi - do show less variations between species and sexes than enzymes not directly involved in specialized functions...

Ecto-enzyme of granulocytes: 5'-nucleotidase

The 5'-nucleotidase of guinea pig polymorphonuclear leukocytes is localized exclusively on the plasma membrane of intact cells. The active site of this enzyme faces the external medium, not the cytoplasm.

Biochemical localization of alkaline phosphatase in the cell wall of a marine pseudomonad

The various layers of the cell envelope of marine pseudomonad B-16 (ATCC 19855) have been separated from the cells and assayed directly for alkaline phosphatase activity under conditions established previously to be optimum for maintenance of the activity of the enzyme. Under conditions known to lead to the release of the contents of the periplasmic space from the cells, over 90% of the alkaline phosphatase was released into the medium. Neither the loosely bound outer layer nor the outer double-track layer (cell wall membrane) showed significant activity. A small amount of the alkaline phosphatase activity of the cells remained associated with the mureinoplasts when the outer layers of the cell wall were removed. Upon treatment of the mureinoplasts with lysozyme, some alkaline phosphatase was released into the medium and some remained with the protoplasts formed. Cells washed and suspended in 0.5 M NaCl were lysed by treatment with 2% toluene, and 95% of the alkaline phosphatase in the cells was released into the medium. Cells washed and suspended in complete salts solution (0.3 M NaCl, 0.05 M MgSO(4), and 0.01 M KCl) or 0.05 M MgSO(4) appeared intact after treatment with toluene but lost 50 and 10%, respectively, of their alkaline phosphatase. The results suggest that the presence of Mg(2+) in the cell wall is necessary to prevent disruption of the cells by toluene and may also be required to prevent the release of alkaline phosphatase by toluene when disruption of the cells by toluene does not take place.