Molecular extinction coefficients of lead sulfide and polymerized diaminobenzidine as final reaction products of histochemical phosphatase reactions

Meijer and Vloedman's histochemical demonstration of mitochondrial coupling obeys Lambert-Beer's law in the myocardium

Uncoupling of mitochondrial proton pumping and adenosine triphosphate (ATP) production lowers mitochondrial efficiency. Current methods to determine mitochondrial efficiency require substantial amounts of tissue and permeabilization or isolation procedures. A simple histochemical method has been described by Meijer and Vloedman (Histochemistry 69:217–232, 1980, 10.1007/BF00489769), but this was not quantitative. We found linear correlations between (1) absorbance and sections thickness and (2) absorbance and incubation time. Because the method obeys Lambert–Beer’s law, we can estimate ATP/O₂ ratios for healthy and overloaded right-sided rat myocardium. We related mitochondrial efficiency to the ratio between cardiolipin and its precursor phosphatidylglycerol. We found a non-linear relationship between mitochondrial efficiency and this ratio, indicating that lower mitochondrial efficiency as found in experimental pulmonary hypertension may be due to altered composition of the mitochondrial inner membrane. We conclude that the histochemical method of Meijer and Vloedman can be applied to quantify mitochondrial efficiency.

Phosphohydrolytic activity in Paramecium caudatum at neutral pH

Phosphohydrolytic activity was cytochemically characterized in Paramecium caudatum, a ciliated protozoa, at neutral pH. We stained cells in the presence of several mononucleotides as substrates, namely adenosine 5'-monophosphate (5'-AMP), adenosine 2'-monophosphate, guanosine 5'-monophosphate (5'-GMP) and beta-glycerophosphate (beta-GLP) using a lead capture method at 37 degrees C. Cells were also incubated in the presence of 5'-AMP with the inhibitor for alkaline phosphatase, tetramisole. In all cases, varying amounts of final reaction product, lead sulfide, was observed in Paramecium cytoplasm. Tetramisole did not have any effect on Paramecium 5'-AMP hydrolytic activity. The phosphohydrolytic activity was measured as the increase in total absorbance of "test minus control" reactions at 440 nm per unit time after 20 min of incubation using a microphotometric system for image analysis that has been developed by us. From the relationship between the concentrations of 5'-AMP and activity, an apparent K(m) value was estimated to be 0.20 mM. These results suggest that mononucleotides and phosphate monoesters are hydrolyzed by one or more enzymes with wide substrate specificity in P. caudatum. All the activity distribution patterns in Paramecium cultures, that were tested, were monomodal. The mean activity for 5'-AMP hydrolysis widely varied in these cultures. To investigate substrate affinity, distribution patterns and mean activity with 5'-AMP as substrate were compared with those in the presence of 2 other substrates, 5'-GMP and beta-GLP. Affinity of the enzyme(s) was similar for 5'-AMP and 5'-GMP and lower for beta-GLP.

Extinction coefficient of polymerized diaminobenzidine complexed with cobalt as final reaction product of histochemical oxidase reactions

The extinction coefficient is essential for the conversion of cytophotometric (mean integrated) absorbance values into absolute units of enzyme activity, for instance expressed in terms of moles of substrate converted per unit time and per unit wet weight of tissue. The extinction coefficient of polymerized diaminobenzidine (polyDAB) complexed with cobalt as the final reaction product of oxidase reactions was estimated at 575 nm by comparison of the amounts of final reaction products formed after incubation of serial unfixed cryostat sections of rat kidney to demonstrate D-amino acid oxidase activity with either the tetrazolium salt method or the cerium-DAB-cobalt-hydrogen peroxide method. Both procedures resulted in similar localization patterns of final reaction product in a granular form in epithelial cells of proximal tubules in rat kidney. The granules were peroxisomes. Linear relationships were found for both methods between the specific amounts of final reaction product generated by D-amino acid oxidase activity and incubation time. The cerium salt method gave rise to 7.4 times higher absorbance values of final reaction product generated per unit time and per unit wet weight of tissue than the tetrazolium salt procedure. The extinction coefficient of tetranitro BT-formazan is 19,000 at 557 nm. Therefore, the cytophotometric extinction coefficient of the polyDAB-cobalt complex as final reaction product of oxidase reactions was established to be 140,000.

Analysis of enzyme reactions in situ

Estimations of metabolic rates in cells and tissues and their regulation on the basis of kinetic properties of enzymes in diluted solutions may not be applicable to intact living cells or tissues. Enzymes often behave differently in living cells because of the high cellular protein content that can lead to homologous and heterologous associations of protein molecules. These associations often change the kinetics of enzymes as part of post-translational regulation mechanisms. An overview is given of these interactions between enzyme molecules or between enzyme molecules and structural elements in the cell, such as the cytoskeleton. Biochemical and histochemical methods are discussed that have been developed for in vivo and in situ analyses of enzyme reactions, particularly for the study of effects of molecular interactions. Quantitative (histochemical) analysis of local enzyme reactions or fluxes of metabolites has become increasingly important. At present, it is possible to calculate local concentrations of substrates in cells or tissue compartments and to express local kinetic parameters in units that are directly comparable with those obtained by biochemical assays of enzymes in suspensions. In situ analysis of the activities of a number of enzymes have revealed variations in their kinetic properties (Km and Vmax) in different tissue compartments. This stresses the importance of in vivo or in situ analyses of cellular metabolism. Finally, histochemical determinations of enzyme activity in parallel with immunohistochemistry for the detection of the total number of enzyme molecules and in situ hybridization of its messenger RNA allow the analysis of regulation mechanisms at all levels between transcription of the gene and post-translational activity modulation.

Quantitative comparison between the gel-film and polyvinyl alcohol methods for dehydrogenase histochemistry reveals different intercellular distribution patterns of glucose-6-phosphate and lactate dehydrogenases in mouse liver

The precise histochemical localization and quantification of the activity of soluble dehydrogenases in unfixed cryostat sections requires the use of tissue protectants. In this study, two protectants, polyvinyl alcohol (PVA) and agarose gel, were compared for assaying the activity of lactate dehydrogenase (LDH) and glucose-6-phosphate dehydrogenase (G6PDH) in normal female mouse liver. Quantification of enzyme activity was determined cytophotometrically in periportal (PP), pericentral (PC) and midzonal (MZ) areas. No coloured reaction product was present in PVA media after the incubation period. In contrast, the agarose gels appeared to be highly coloured after incubation. As a consequence, sections incubated with gel media were less intensely stained than those incubated in PVA-containing media. The specific G6PDH reaction (test minus control) yielded approximately 75% less formazan in sections incubated by the agarose gel method than with the PVA method. Further, the amount of formazan deposits attributable to G6PDH activity was highest in the midzonal and pericentral zones of the liver lobule with PVA media, and Kupffer cells could be discriminated easily because of their high G6PDH activity. Significant zonal differences or Kupffer cells could not be observed when agarose gel films were used for the detection of G6PDH activity. The LDH localization patterns appeared to be more uniform after incubation with both methods: no significant differences in specific test minus control reactions were seen between PP, PC and MZ. However, less formazan production (33%) was detected in sections incubated with agarose gels when compared with those incubated with PVA media.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerium methods for light and electron microscopical histochemistry

Methods based on the use of cerium to detect the activity of oxidases and phosphatases are rapidly expanding. Both classes of enzymes can be demonstrated with cerium at the electron and light microscopical level. The in situ detection of H2O2 production with cerium is another application that has great potential, particularly in experimental pathological research. The fine precipitate of the cerium-containing final reaction product, cerium perhydroxide or cerium phosphate, enables a very precise localization. With such techniques, important advances have been made in cell biology, such as the discovery of new organelles, functional subcompartmentization of peroxisomes, tubular lysosomes and the elucidation of the function of extracellular ATPases. At the light microscopical level, the activity of enzymes can be quantified in situ because the production of final reaction product in the cerium methods is proportional to enzyme activity in tissue sections or cells. Cerium precipitates have strong reflectance properties and this enables their use in confocal scanning laser microscopy. In the present review, the principles of cerium methods are outlined and applications in cell biology and pathology are discussed.

Quantitative determination of calcium-activated myosin adenosine triphosphatase activity in rat skeletal muscle fibres

A quantitative histochemical technique was developed for determining the kinetics of the calcium-activated myosin ATPase (Ca(2+)-myosin ATPase) reaction in rat skeletal muscle fibres. Using this technique, the maximum velocity (Vmax) and the apparent Michaelis-Menten rate constant for ATP (K(app)) of the Ca(2+)-myosin ATPase reaction were measured in type-identified fibres of the rat medial gastrocnemius (MG) muscle. The Vmax and the K(app) of the Ca(2+)-myosin ATPase reaction were lowest in type I fibres and highest (i.e., approx. two times greater) in type IIb fibres. The K(app) in type IIa fibres was similar to that in type I. However, the Vmax was 1.5 times greater in type IIa fibres, compared to type I fibres. Evidence is presented to suggest that the type IIb fibre population in the MG does not represent a single myosin isozyme. In addition, the broad range of Vmax and K(app) values indicates that there is marked heterogeneity in the myosin heavy chain and myosin light chain composition of myosin isozymes among individual fibres.