Oxidation of phosphatidylserine: a mechanism for plasma membrane phospholipid scrambling during apoptosis?

Selective oxidation of phosphatidylserine (PS) during apoptosis precedes its externalization in plasma membrane and is essential for the engulfment of apoptotic cells. To experimentally test whether PS oxidation stimulates its externalization via its effects on aminophospholipid translocase (APT) or by enhanced PS scrambling, action of oxidized PS (PSox) was studied using leukemia HL-60 cells and lymphoma Raji cells. Both PS and PSox were equally well recognized by APT. PSox did not inhibit APT. Rate of transmembrane PS diffusion was fourfold higher in cells with integrated PSox than with PS. Thus, PSox acts as a "non-enzymatic scramblase" likely contributing to PS externalization.

Lipid antioxidant, etoposide, inhibits phosphatidylserine externalization and macrophage clearance of apoptotic cells by preventing phosphatidylserine oxidation

Apoptosis is associated with the externalization of phosphatidylserine (PS) in the plasma membrane and subsequent recognition of PS by specific macrophage receptors. Selective oxidation of PS precedes its externalization/recognition and is essential for the PS-dependent engulfment of apoptotic cells. Because etoposide is a potent and selective lipid antioxidant that does not block thiol oxidation, we hypothesized that it may affect PS externalization/recognition without affecting other features of the apoptotic program. We demonstrate herein that etoposide induced apoptosis in HL-60 cells without the concomitant peroxidation of PS and other phospholipids. HL-60 cells also failed to externalize PS in response to etoposide treatment. In contrast, oxidant (H2O2)-induced apoptosis was accompanied by PS externalization and oxidation of different phospholipids, including PS. Etoposide potentiated H2O2-induced apoptosis but completely blocked H2O2-induced PS oxidation. Etoposide also inhibited PS externalization as well as phagocytosis of apoptotic cells by J774A.1 macrophages. Integration of exogenous PS or a mixture of PS with oxidized PS in etoposide-treated HL-60 cells reconstituted the recognition of these cells by macrophages. The current data demonstrate that lipid antioxidants, capable of preventing PS peroxidation, can block PS externalization and phagocytosis of apoptotic cells by macrophages and hence dissociate PS-dependent signaling from the final common pathway for apoptosis.

Inhibition of membrane-bound succinate dehydrogenase by fluorescamine

Fluorescamine rapidly inactivated membrane-bound succinate dehydrogenase. The inhibition of the enzyme by this reagent was prevented by succinate and malonate, suggesting that the group modified by fluorescamine was located at the active site. The modification of the active site sulfhydryl group by 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) did not alter the inhibitory action of fluorescamine. However, the protective effect of malonate against fluorescamine inhibition was abolished in the enzyme modified at the thiol.

Fluorescamine-induced membrane permeability in mitochondria

1. Addition of fluorescamine (75 microM) to mitochondria induced an increase in membrane permeability. 2. The leakiness of the inner mitochondrial membrane is characterized by extensive release of accumulated Ca2+, collapse of the transmembrane potential, mitochondrial swelling and efflux of matrix proteins, among them, malate dehydrogenase. 3. These effects were diminished by supplementing the media with 1 mM phosphate, and partially prevented by Mg2+. 4. These results indicate that the primary amino groups of membrane components contribute, partially, to the maintenance of the permeability barrier in mitochondria.

Fluram induces species-dependent C and G bands in mammalian chromosomes, revealing heterogeneous distribution of chromosomal proteins

Fluram (Fluorescamine; 4-phenylspiro(furan-2(3H),1'-phthalan)-3,3'-dione) is a fluorogenic reagent, which permits the detection of primary amines by forming highly fluorescent pyrrolinone derivatives. This reagent has been used on methanol-acetic acid fixed metaphase chromosomes of mouse and man and proved to be very effective in differentiating chromosome regions in both genomes. Mouse centromeric heterochromatin is highly reactive, showing intense fluorescence in all centromeric regions, whereas human chromosomes show no fluorescence in such regions. In addition, a G-like banding pattern is also obtained in both types of chromosomes. The differential reactivity of each chromosome region showed by this method demonstrates a heterogeneous distribution of chromosome proteins, resulting in a chromosome banding pattern, which is in this case species dependent.

Heat-induced alterations in monkey erythrocyte membrane phospholipid organization and skeletal protein structure and interactions

Rhesus monkey erythrocytes were subjected to heating at 50 degrees C for 5-15 min, and the heat-induced effects on the membrane structure were ascertained by analysing the membrane phospholipid organization and membrane skeleton dynamics and interactions in the heated cells. Membrane skeleton dynamics and interactions were determined by measuring the Tris-induced dissociation of the Triton-insoluble membrane skeleton (Triton shells), the spectrin-actin extractability at low ionic strength, spectrin self-association and spectrin binding to normal monkey erythrocyte membrane inside-out vesicles (IOVs). The Tris-induced Triton shell dissociation and spectrin-actin extractability were markedly decreased by the erythrocyte heating. Also, the binding of the heated erythrocyte membrane spectrin-actin with the IOVs was much smaller than that observed with the normal erythrocyte spectrin-actin. Further, the spectrin structure was extensively modified in the heated cells, as compared to the normal erythrocytes. Transbilayer phospholipid organization was ascertained by employing bee venom and pancreatic phospholipases A2, fluorescamine, and Merocyanine 540 as the external membrane probes. The amounts of aminophospholipids hydrolysed by phospholipases A2 or labeled by fluorescamine in intact erythrocytes considerably increased after subjecting them to heating at 50 degrees C for 15 min. Also, the fluorescent dye Merocyanine 540 readily stained the 15-min-heated cells but not the fresh erythrocytes. Unlike these findings, the extent of aminophospholipid hydrolysis in 5-min-heated cells by phospholipases A2 depended on the incubation time. While no change in the membrane phospholipid organization could be detected in 10 min, prolonged incubations led to the increased aminophospholipid hydrolysis. Similarly, fluorescamine failed to detect any change in the transbilayer phospholipid distribution soon after the 5 min heating, but it labeled greater amounts of aminophospholipids in the 5-min-heated cells, as compared to normal cells, after incubating them for 4 h at 37 degrees C. These results have been discussed to analyse the role of membrane skeleton in maintaining the erythrocyte membrane phospholipid asymmetry. It has been concluded that both the ATP-dependent aminophospholipid pump and membrane bilayer-skeleton interactions are required to maintain the transbilayer phospholipid asymmetry in native erythrocyte membrane.

Purification and properties of isopenicillin N epimerase from Streptomyces clavuligerus

Isopenicillin N epimerase, which catalyzes conversion of isopenicillin N to penicillin N, has been purified to electrophoretic homogeneity from the cell-free extract of Streptomyces clavuligerus by a procedure involving ammonium sulfate fractionation and chromatographies with DE-52, DEAE Affi-gel blue, Sephadex G-200, calcium phosphate-cellulose, and Mono Q. The purified epimerase is monomeric with a molecular weight of 47,000 or 50,000 as estimated by SDS-polyacrylamide gel electrophoresis or gel filtration, respectively. The enzyme contains 1 mol of pyridoxal 5'-phosphate per mol of protein, and shows absorption maxima at 280 and 420 nm. The epimerase catalyzes the complete 'racemization' on both the L-alpha-aminoadipyl side-chain of isopenicillin N and the D-alpha-aminoadipyl side-chain of penicillin N, so that an approximately equimolar mixture of the two penicillins is produced. The mixture is not truly racemic, since these penicillins are diastereomers rather than optical isomers. The chemical modification of primary amino groups of the epimerase by fluorescamine results in a great loss of the enzyme activity. The activity of purified enzyme is partially stimulated by the addition of sulfhydryl compounds. The activity is strongly inhibited by sulfhydryl group modifiers such as p-chloromercuribenzoate and N-ethylmaleimide.

Effect of chemical modification on the crystallization of Ca2+-ATPase in sarcoplasmic reticulum

The influence of chemical modification on the morphology of crystalline ATPase aggregates was analyzed in sarcoplasmic reticulum (SR) vesicles. The Ca2+-ATPase forms monomer-type (P1) type crystals in the E1 and dimer-type (P2) crystals in the E2 conformation. The P1 type crystals are induced by Ca2+ or lanthanides; P2 type crystals are observed in Ca2+-free media in the presence of vanadate or inorganic phosphate. P1- and P2-type Ca2+-ATPase crystals do not coexist in significant amounts in native sarcoplasmic reticulum membrane. The crystallization of Ca2+-ATPase in the E2 conformation is inhibited by guanidino-group reagents (2,3-butanedione and phenylglyoxal), SH-group reagents, phospholipases C or A2, and detergents, together with inhibition of ATPase activity. Amino-group reagents (fluorescein 5'-isothiocyanate, pyridoxal phosphate and fluorescamine) inhibit ATPase activity but do not interfere with the crystallization of Ca2+-ATPase induced by vanadate. In fluorescamine-treated sarcoplasmic reticulum the vanadate-induced crystals contain significant P1-type regions in addition to the dominant P2 form.

Chemical modification of dopamine beta-hydroxylase

Dopamine beta-hydroxylase (3,4- dihydroxyphenylethylamine ,ascorbate:oxygen oxidoreductase (beta-hydroxylating), EC 1.14.17.1) is the terminal enzyme in the biosynthetic pathway of norepinephrine. Chemical modification studies of this enzyme were executed to investigate contributions of specific amino-acid side-chains to catalytic activity. Sulfhydryl reagents were precluded, since no free cysteine residue was detected upon titration of the denatured or native protein with 2-chloromercuri-4-nitrophenol. Incubation of enzyme with diazonium tetrazole caused inactivation of the protein coupled with extensive reaction of lysine and tyrosine residues. Reaction with iodoacetamide resulted in complete loss of enzymatic activity with reaction of approximately three histidine residues; methionine reaction was also observed. Modification of the enzyme using diethylpyrocarbonate resulted in complete inactivation of the enzyme, and analysis of the reacted protein indicated a loss of approx. 1.7 histidine residues per protein monomer with no tyrosine or lysine modification observed. The correlation of activity loss with histidine modification supports the view that this residue participates in the catalytic function of dopamine beta-hydroxylase.

Amine fluorescamine compounds inhibit oxidative phosphorylation in rat liver mitochondria

The reaction of fluorescamine with ammonia, benzylamine, o,p-dimethylbenzylamine, 2-phenylethylamine, p-aminobenzoic acid, and the mycosamine-containing macrolide antibiotic, amphotericin B, yield compounds which induce significant effects on mitochondrial activities. From their effects on energy-yielding processes which lead to transmembranous proton movements, the compounds may be divided into three classes. While all modifiers significantly inhibit proton movement induced by both ATP hydrolysis and electron transfer in mitochondria, their influence on the primary energy yielding steps are quite different. Class I modifiers, e.g., the compound made from amphotericin B, inhibit electron transfer but have no effect on the Pi release associated with ATP hydrolysis. Class II modifiers, e.g., the compound made from benzylamine, inhibit respiration but stimulate Pi release. Class III modifiers, e.g., the compound made from p-aminobenzoic acid, on the other hand, only slightly increase Pi release but have no effect on redox reactions. These and other effects of the modifiers are taken to mean that the proton movements and their associated energy-yielding processes are only linked indirectly. The effects of the modifiers on State 3 mitochondrial activities were also investigated. Although all the modifiers decrease the rates of both State 3 respiration and its coupled ATP synthesis, the efficiency of energy conversion measured by the P/O ratio remains unaltered.

[Structural changes in erythrocyte ghosts after irradiation and the initiation of lipid oxidation detectable using 2,6-TNS and fluorescamine]

It was shown on erythrocyte ghosts that the parameters of fluorescence of 2,6-toluidine-naphthalene-sulfonate (2,6-TNS) and fluorescamine undergo similar changes after irradiation. After a dose of 100 Gy the equally effective concentrations of Fe2+ were 1-5 microM and 50-100 microM with regard to changes in the rate of fluorescence of fluorescamine and 2,6-TNS, respectively, and greater than 100 microM with regard to fluorescence anisotropy.

The effect of malonyldialdehyde, a product of lipid peroxidation, on the deformability, dehydration and 51Cr-survival of erythrocytes

Erythrocyte membrane lipid peroxidation has been reported to occur in various haemolytic anaemias. In the present study, treatment of human erythrocytes with malonyldialdehyde (MDA), a product of fatty acid peroxidation, induced membrane rigidity, cellular dehydration and reduced whole cell deformability. These effects of MDA were blocked by histamine and fluorescamine, which can act as alternate substrates for MDA. Additionally, reduced deformability of MDA-treated rabbit cells was associated with shortened 51Cr survival in vivo. These findings suggest a biochemical basis for decreased survival of erythrocytes undergoing peroxidative damage of the membrane.

Uncoupling of Ca2+ transport in sarcoplasmic reticulum as a result of labeling lipid amino groups and inhibition of Ca2+-ATPase activity by modification of lysine residues of the Ca2+-ATPase polypeptide

Limited labeling of amino groups with fluorescamine in fragmented sarcoplasmic reticulum vesicles inhibits Ca2+-ATPase activity and Ca2+ transport. Under the labeling conditions used, 80% of the label reacts with phosphatidylethanolamine and 20% with the Ca2+-ATPase polypeptide. This degree of labeling does not result in vesicular disruption or in loss of vesicular proteins and does not increase the membrane permeability to Ca2+. Fluorescamine labeling of a purified Ca2+-ATPase devoid of aminophospholipids also inhibits Ca2+-ATPase activity, suggesting that labeling of lysine residues of the enzyme polypeptide is responsible for the inhibition of Ca2+-ATPase activity in sarcoplasmic reticulum. Fluorescamine labeling interferes with phosphoenzyme formation and decomposition in both the native vesicles and the purified enzyme; addition of ATP during labeling, and with less effectiveness ADP or AMP, protects both partial reaction steps. Addition of a nonhydrolyzable ATP analog protects phosphoenzyme formation but not decomposition. The inhibition of Ca2+ transport but not of Ca2+-ATPase occurs in sarcoplasmic reticulum vesicles labeled in the presence of ATP, indicating that the transport reaction is uncoupled from the Ca2+-ATPase reaction. The inhibition of Ca2+ transport but not of Ca2+-ATPase activity is also found in sarcoplasmic reticulum vesicles in which only phosphatidylethanolamine has reacted with fluorescamine. Furthermore, the extent of labeling of phosphatidylethanolamine is correlated with the inhibition of Ca2+ transport rates. The inhibition of Ca2+ transport is a reflection of the inhibition of Ca2+ translocation and is not due to an increase in Ca2+ efflux. We propose that labeling of phosphatidylethanolamine perturbs the lipid environment around the enzyme, producing a specific defect in the Ca2+ translocation reaction.

Effects of borohydride-treated oligomycins on processes of energy transduction in mitochondria

Sodium borohydride in ethanol solution under mild conditions brings about the stepwise reduction of the 7-keto and the 11-keto groups of rutamycin and the oligomycins to the corresponding hydroxyl groups without further alterations of the macrocyclic lactone structure or other features of the molecule. The reduced compounds, as well as the parent antibiotics, inhibit the ADP-dependent (state 3) respiration, and the Pi formation and proton extrusion that are linked to ATP hydrolysis, but have no effect on other respiration-linked activities in intact rat liver mitochondria. Analogous inhibitory effects of borohydride-treated antibiotics are also observed in rat-liver submitochondrial particles. The reduced compounds are less potent inhibitors than the parent antibiotics. The reduced compounds are more efficient as inhibitors of Pi formation stimulated by conventional uncouplers (e.g. 2,4-dinitrophenol), than of Pi formation stimulated by certain amine-fluorescamine modifiers (e.g.) the benzylamine-fluorescamine compound. In contrast, the parent antibiotics are unable to discriminate between uncoupler-stimulated and modifier-stimulated Pi formation. It is suggested that rutamycin and the oligomycins bind to H+-ATPase as a result of hydrogen bonding to, at least, the 7-keto and/or the 11-keto groups of the antibiotics. When these keto groups are reduced to hydroxyl groups the hydrogen-bonding is less efficient due to the pronounced directional characteristic of hydrogen-bonding to keto groups.

Activity of phospholipase A2 in the inner membrane of rat-liver mitochondria

The inner membrane of rat liver mitochondria contains a highly active phospholipase A2 which has alkaline pH optimum and requires Ca2+ in the micromolar range. The phospholipase is particularly active on the endogenous phosphatidylethanolamine and release relatively high amounts of docosahexanoic acid. The phospholipase A2 of mitochondria or mitoplasts is not dependent on calmodulin. Using fluorescamine-labelled mitoplasts there are indications that the enzyme is localized on both sides of the inner membrane.

The participation of primary amino groups of succinate dehydrogenase in the formation of succinate-Q reductase

(1) Purified succinate dehydrogenase contains about 49 mol of lysine residues per mol enzyme. Titration of succinate dehydrogenase with fluorescamine indicates that half the lysyl groups are located on the surface of the protein and the other half are buried inside. (2) The reconstitutive activity and the low Km ferricyanide reductase activity of succinate dehydrogenase decreased as the extent of alkylation of amino groups by fluorescamine increased. (3) The inhibitory effects of fluorescamine on both activities are parallel and are succinate concentration dependent. (4) Alkylation of the native succinate-Q reductase by fluorescamine does not affect the enzymatic activity or alter the enzyme kinetic parameters. This indicates that the inhibitory effect of fluorescamine on succinate dehydrogenase is due to the modification of a specific amino group(s) on succinate dehydrogenase which is essential in the interaction with QPs to form succinate-Q reductase. The participation of an ionic group in the formation of succinate-Q reductase supports the idea of the involvement of ionic interaction between succinate dehydrogenase and QPs.

Inhibition of the links between electron transfer and proton translocation in mitochondria

The mechanism by which proton extrusion is linked to electron transfer in mitochondria was investigated by means of the primary amine-specific reagent fluorescamine, and of compounds obtained from the reaction of fluorescamine with simple amines (e.g. benzylamine) and with the mycosamine-containing antibiotic amphotericin B. The effect of these 'modifiers' (i.e. fluorescamine transfer chain were assayed separately using specific inhibitors to block the action associated with the other site. Both types of modifiers inhibited the proton extrusion across the membrane to a significantly greater extent than the electron transfer process in both sites II and III. In contrast, the lactone derivative (or cyclic form) of the amine-fluorescamine compounds had no significant inhibitory effect on the proton extrusion and its associated electron transfer. These results are consistent with the hypothesis that the link between proton extrusion and electron transfer in mitochondria is indirect in nature. The results show that: (a) the links involved in sites II and III are identical or very similar in nature; (b) a covalent modification of primary amino groups in the inner membrane is not essential for the expression of these differential inhibitory effects; (c) specific structural features in the amine-fluorescamine compounds, and in the mitochondria-fluorescamine derivatives, are crucial for the expression of the inhibitory effects. Our results contradict the 'redox loop' model of Mitchell, and are compatible with the proton pump concept for the linked proton translocation in oxidative phosphorylation.

The inhibition of the calcium transport ATPase of the sarcomplasmic reticulum by fluorescamine: evidence for an oligomeric functional unit of the calcium transport system

The labeling of the protein moiety of the sarcoplasmic calcium transport ATPase by fluorescamine suppresses calcium transport, calcium dependent ATPase activity, protein phosphorylation by [gamma-32P]ATP and [32P]phosphate at different extent of amino group substitution. For the hydrolysis of para nitrophenylphosphate by the calcium transport ATPase, it is shown that the relationship between the extent of amino group labelling can considerably be altered by the temperature and the presence of ethyleneglycol. It is shown that the amino residues of the phosphatidylethanolamine moiety do not contribute to the inhibiting effect of fluorescamine labelling. The observations suggest that the different functions of the calcium transport system are based on the cooperation of a varying number of calcium transport ATPase molecules.

Differential effects on energy transduction processes by fluorescamine derivatives in rat liver mitochondria

Intact rat liver mitochondria were treated with compounds derived from the reaction of fluorescamine with various types of primary amines, including the mycosamine-containing antibiotics amphotericin B and nystatin. The effect of varying amounts of these compounds on ATPase-linked inorganic phosphate (Pi) formation on oxygen consumption, and on MgATP-linked and succinate-linked proton movements was examined. The antibiotic-fluorescamine compounds did not affect the Pi formation rate but strongly inhibited both the ATPase-linked and the succinate-linked H+ extrusion rates to approximately the same extent. The antibiotic derivatives decreased the oxygen consumption rate, but this effect was much smaller than the decrease in the respiration-dependent proton extrusion rate. The benzylamine-fluorescamine compound significantly increased the Pi formation rate, in contrast to the antibiotic analogues. The benzylamine derivative, like the antibiotic derivatives, inhibited both types of proton extrusion rates. The slight decrease in the oxygen consumption rate caused by the benzylamine derivative was significantly smaller than the corresponding decrease observed with the antibiotic derivatives. These studies, in which fluorescamine derivatives bind reversibly to mitochondria, are compared with previous studies in which fluorescamine itself binds irreversibly to mitochondria and results in a Pi formation rate increase and MgATP- and succinate-linked proton extrusion rate inhibition but has no effect on the oxygen consumption rate.

A possible preferential inhibition of chemotaxis of polymorphonuclear neutrophils by a chemical modification

The modification of neutrophils with amino group blocking reagents of different chemical specificities showed that dansyl chloride caused inhibition of chemotaxis without suppression of random movement. Dansylated neutrophils, like control cells, ingested bacteria. Neither the stimulated cyanide-insensitive respiration, nor lactate production during phagocytosis, was affected significantly by dansylation as compared with the inhibition of directed movement.

Fluorescent labelling of proteins of lymphocyte plasma membranes

Fluorescamine has been used for labelling proteins present on the surface of normal human peripheral blood lymphocytes. Under the conditions of study, 12 labelled proteins could be detected by SDS gel electrophoresis. This method may be of value in biochemical studies of lymphocyte membranes.

The effect of sulfhydryl and amino group reagents on human lymphocyte--sheep erythrocyte rosettes

We have studied the influence of certain chemical groups, located on the surface of lymphocytes or sheep red blood cells, on the ability of these cells to form spontaneous rosettes. We found that fluorescamine, which reacts with amino groups, inhibits rosette formation, while p-chloromercuriphenylsulfonic acid, which binds to sulfydryl groups, increases the percentage of the rosette-forming lymphocytes. The possible mechanism of action of the above reagents is discussed.

Participation of X47-fluorescamine modified E. coli tRNAs in in vitro protein biosynthesis

The reaction of fluorescamine with primary amino groups of tRNAs was investigated. The reagent was attached under mild conditions to the 3'-end of tRNAPhe-C-C-A(3'NH) from yeast and to the minor nucleoside x in E. coli tRNAArg, tRNALys, tRNAMet, tRNAIle and tRNAPhe. The primary aliphatic amino groups of these tRNAs react specifically so that the fluorescamine dye is not attached to the amino groups of the nucleobases. E. coli tRNA species modified on the minor nucleoside X47 can all be aminoacylated. An involvement of the minor modified nucleoside X47 in the tRNA: synthetase interaction is detected. Native tRNALys-C-C-A from E. coli can be phenylalanylated by phenylalanyl-tRNA synthetase from yeast, whereas this is not the case for fluorescamine treated tRNALys-C-C-A(XF47). Pre-tRNAPhe-C-C-A(XF47) forms a ternary complex with the elongation factor Tu:GTP from E. coli, binds enzymatically to the ribosomal A-site and is active in poly U dependent poly Phe synthesis. Fluorescamine-labelled E. coli tRNAs provide new substrates for the study of protein biosynthesis by spectroscopic methods.

The influence of enzymatic cleavage and chemical modification of human and rabbit IgG on their reactivity with staphylococcal protein A

Proteolytic cleavage fragments from rabbit IgG have been isolated and characterized in an attempt to locate the sites involved in the reactivity with Staphylococcal protein A. The plasmin cleavage product Facb together with the pepsin cleavage products F(ab')2 and pFc' failed to react in contrast to the papain Fc fragment. These data, together with data from unfractionated plasmin digests, in which the Facb fragment remains associated with the plasmin pFc' fragment, indicate that inter-domain interactions are important in the maintenance of this activity. beta2-microglobulin was also shown to be unreactive with protein A. Chemical modification studies employing flurescamine, tetranitromethane and potassium cyanate indicate that lysine and tyrosine residues are not involved in the reactivity of human and rabbit IgG with protein A.

Effect of chemical modification of amino groups by fluorescamine on partial reactions of photosynthesis

4-Phenylspiro [furan-2(3H),1-phtalan]3,3'-dione (fluorescamine) was used to covalently modify amino groups of thylakoids. Subsequently its effect on parameters of energy transfer and phosphorylating activity was assessed. While electron transport, the extent of proton uptake, 515 nm change and 9-aminoacridine quench were relatively resistant to such treatment, the functions connected to coupling factor 1, namely ATP formation by acid/base transition, ATPase activity and photophosphorylation were affected much earlier. Photophosphorylation appears to be the most sensitive. The data are interpreted as indicating an involvement of free amino groups in energy transfer.

Microspectrography of formaldehyde and fluorescamine-induced fluorescence in rabbit pulmonary neuroepithelial bodies: demonstration of a new, probably polypeptide intracytoplasmic substance

The microspectrographic analysis of the fluorescence emitted by NEB's in gaseous formaldehyde-fixed lung tissue, posttreated with fluorescamine, revealed the presence of numerous primary amino groups which are clearly different from the serotonin identified in our earlier studies and correspond to a new, probably a polypeptide intracytoplasmic substance.

The functional and fluorescence properties of Escherichia coli RNA polymerase reacted with fluorescamine

1. Fluorescamine (4-phenylspiro[furan-2,(3)1'-phthalan]-3,3'-dione) reacts rapidly with Escherichia coli RNA polymerase and produces a fluorescent derivative which is inactivated to an extent dependent upon reagent concentration. Excess fluorescamine is rapidly hydrolysed. Reaction is with xi-amino gruops of lysine residues in all subunits as revealed by gel electrophoresis and fluorescence scanning. 2. The extent of inactivation and fluorescence yield are diminished in the presence of added template, a finding which provides evidence for the existence of reactive and essential amino groups which can be at least partially shielded by DNA in the binary complexes. The relative decrease of fluorescence is greatest in the betabeta' subunits. Holoenzyme and core enzyme show essentially the same behavior. 3. The inactivation of activity by fluorescamine is primarily at the level of initiation. Template binding and chain propagation are less affected. 4. The enzyme derivatized by fluorescamine shows an intense fluorescence with a peak at 490 nm and an excitation maximum at 390 nm. The fluorescence lifetime is in the range of 3-8 ns and the emission is highly polarized. In reactions carried out at high ionic strength the fluorescence yield is approximately double that at low ionic strength and insensitive to the presence of template. 5. Energy transfer is observed between the derivatized enzyme as donor and ethidium bromide as acceptor in the presence of template to which both the enzyme and intercalating dye are bound. The transfer efficiency is a function of the relative concentrations and of the conditions of reaction with fluorescamine. An average transfer distance of approx. 4-5 nm has been calculated suggesting a close proximity between bound polymerase and helical regions of the template.