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E Pick

Publications and source records attributed to E Pick.

At least 19 recordsLinked to original sources
PubMed1995

"Peptide walking" is a novel method for mapping functional domains in proteins. Its application to the Rac1-dependent activation of NADPH oxidase.

Activation of the superoxide generating NADPH oxidase of phagocytes involves the assembly of a multimolecular complex and is dependent on the participation of the small molecular weight GTP-binding protein Rac (1 or 2). This model system was used for mapping functional domains in the primary sequence of Rac1, based on assessing the inhibitory effect of 90 individual overlapping pentadecapeptides, spanning the entire length of Rac1, on NADPH oxidase activation in two types of cell-free assay. Five functional domains were identified, each consisting of a cluster of contiguous residues shared by members of five groups of overlapping inhibitory peptides. Four of the five domains are exposed on the molecular surface of Rac1 and were not identified previously by mutational analysis; the fifth corresponds to a polybasic motif near the carboxyl terminus, confirming earlier reports. Screening the entire linear sequence of a protein with a battery of overlapping peptides for interference with its ability to interact with upstream or downstream molecules should be of wide applicability as a reliable, fast, and economical method for mapping of functionally relevant domains.

Amino Acid Sequence↗
PubMed1995

Mapping around the Fused locus on mouse chromosome 17.

We have established a high-resolution genetic map of the region surrounding the Fused locus as a first step towards the molecular identification and analysis of this gene. The candidate region has been covered to a large extent by YAC and P1 contigs, and has been partly characterized by pulsed-field gel analysis.

Animals↗
PubMed1991

Purification and characterization of a third cytosolic component of the superoxide-generating NADPH oxidase of macrophages.

Activation of the superoxide (O2-)-generating NADPH oxidase of phagocytes in a cell-free system by anionic amphiphiles requires the participation of both membrane and cytosolic components. We reported that ammonium sulfate fractionation (Pick, E., Kroizman, T., and Abo, A. (1989) J. Immunol. 143, 4180-4187) and affinity chromatography on 2',5'-ADP-agarose (Shaag, D., and Pick, E. (1990) Biochim. Biophys. Acta 1037, 405-412) permit separation of cytosol in two fractions (sigma 1 and sigma 2) that support O2- production by solubilized membrane synergistically. We now describe the purification of sigma 1 to near homogeneity and demonstrate that it represents a cytosolic component distinct from p47-phox and p67-phox, that are both found in fraction sigma 2. Sigma 1 was absolutely required for the full expression of amphiphile-activated NADPH-oxidase activity. This requirement was evident whether sigma 1 was added to cell-free systems composed of: (a) solubilized membrane and a sigma 2-enriched cytosolic fraction, or (b) purified cytochrome b559, incorporated in liposomes, and purified sigma 2. Sigma 1 was purified by a sequence comprising ammonium sulfate fractionation, hydrophobic chromatography on phenyl-Superose, absorption with CM-Sepharose, anion exchange chromatography on DEAE-Sepharose, and gel filtration on Superose 12. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of sigma 1 of maximal purity, under both reducing and nonreducing conditions, demonstrated the presence of two proteins, of 24 and 22 kDa. On gel filtration, sigma 1 was eluted as a symmetrical peak of 46 kDa that by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed the presence of both 24- and 22-kDa bands. We suggest that, in its native form, sigma 1 might represent a complex of the 24- and 22-kDa proteins. The specific roles of each molecule in NADPH oxidase function remain to be determined.

Animals↗
PubMed1991

Activation of the NADPH oxidase involves the small GTP-binding protein p21rac1.

Professional phagocytes, such as neutrophils and monocytes, have an NADPH oxidase that generates superoxide and other reduced oxygen species important in killing microorganisms. Several components of the oxidase complex have been identified as targets of genetic defects causing chronic granulomatous disease. The complex consists of an electron transport chain that has as its substrate cytosolic NADPH and which discharges superoxide into the cavity of the intracellular phagocytic vacuole. The only electron transport component identified so far is a low-potential cytochrome b, apparently the only membrane component required. At least three cytosolic factors are also necessary, two of which, p67phOx and p47phOx, have been identified by their absence in patients with chronic granulomatous disease. A third component, sigma 1, is required for stimulation of oxidase activity in a cell-free system. The active components of purified sigma 1 are two proteins that associate as heterodimers, and here we report that these are the small GTP-binding protein p21rac1 and the GDP-dissociation inhibitor rhoGDI.

Amino Acid Sequence↗
PubMed1991

The membrane-associated component of the amphiphile-activated, cytosol-dependent superoxide-forming NADPH oxidase of macrophages is identical to cytochrome b559.

The superoxide (O2-) forming NADPH oxidase complex of resting phagocytes can be activated in a cell-free system by certain anionic amphiphiles, such as sodium dodecyl sulfate (SDS). For O2- production to occur, the participation of both membrane-associated and cytosol-derived components is required. The purpose of this investigation was to isolate and characterize the membrane component of NADPH oxidase. For this purpose, guinea pig macrophage membranes were extracted with 1 M NaCl, solubilized by 40 mM octyl glucoside, and subjected to a purification sequence consisting of absorption with DEAE-Sepharose, affinity chromatography on heparin-agarose, and chromatography on hydroxylapatite. At each purification step, fractions were assayed for their ability to support SDS-elicited, cytosol-dependent O2- production, following incorporation in liposomes of phosphatidylcholine. We found that membrane oxidase activity copurified strictly with cytochrome b559. Peak hydroxylapatite fractions exhibited specific O2(-)-forming activity in the range of 81-115 mumol of O2-/mg protein/min and a specific cytochrome b559 content of 7-14 nmol of cytochrome b559/mg protein. SDS-polyacrylamide gel electrophoresis analysis of the peak oxidase activity fractions, derived by hydroxylapatite chromatography, revealed essentially two bands that were identified as the beta (54-60 kDa) and alpha (21/22 kDa) subunits of guinea pig cytochrome b559. The relation of the two polypeptides to cytochrome b559 was established by correlation with a spectral signal characteristic of cytochrome b559, immunoblotting with antibodies against defined human cytochrome b559 beta and alpha chain peptides, cross-linking studies, and deglycosylation experiments. Hydroxylapatite-purified membrane oxidase preparations did not contain FAD and were free of cytochrome c reductase activity. Purified membrane oxidase preparations were also capable of cooperating with purified cytosolic components in SDS-elicited cell-free O2- production. We conclude that the membrane-associated component of the O2- generating NADPH oxidase is identical to cytochrome b559.

Animals↗
PubMed1990

Nucleotide binding properties of cytosolic components required for expression of activity of the superoxide generating NADPH oxidase.

The superoxide generating NADPH oxidase was studied in an SDS-activated cell-free system. This system requires the participation of both membranal and cytosolic components. Cytosol derived from elicited peritoneal guinea pig macrophages was fractionated by several nucleotide affinity chromatography procedures. Various such fractionations led to the separation of two distinct factors, both of which are necessary for the activation and/or activity of the superoxide-forming NADPH oxidase. One factor (sigma 2), bound to octyl, 2',5'-ADP-, 5'-ATP-, 5'-GTP-agarose and carboxymethyl-Sepharose but did not bind to hexyl, 5'-AMP-, 5'-ADP- and 5'-GDP-agarose. The other factor (sigma 1) did not bind to any of the above matrices. Subsequent elution of sigma 2 from 2',5'-ADP-agarose was effected by ATP, GTP and NADPH but not by NADH. Elution from GTP-agarose was by ATP and GTP but not by NADPH. Elution from ATP-agarose was by ATP, GTP and also, albeit weakly, by NADPH. The above results suggest that sigma 2 contains a site which recognizes the phosphate group at the ribose 2' position in adenosine, and a site that recognizes purine nucleotide triphosphates.

Adenosine Triphosphate↗
PubMed1990

Activation of the superoxide-generating NADPH oxidase of macrophages by sodium dodecyl sulfate in a soluble cell-free system: evidence for involvement of a G protein.

The superoxide (O2-)-generating NADPH oxidase of resting macrophages can be activated in a soluble cell-free system by certain anionic amphiphiles, such as sodium dodecyl sulfate (SDS). We demonstrate that cell-free activation is specifically enhanced by nonhydrolyzable guanosine 5'-triphosphate (GTP) analogues. Guanosine 5'-diphosphate (GDP) and guanosine 5'-O-(2-thiodiphosphate) (GDP beta S) prevent cell-free oxidase activation and reverse the activated state when added to preactivated oxidase preparations. Nonhydrolyzable GTP analogues have a protective effect on the SDS-stimulated NADPH oxidase, as shown by the maintenance of more than 90% and close to 60% of enzyme activity 6 and 24 hr, respectively, after the addition of SDS to the cell-free preparation. A novel procedure is described for separating the activated NADPH oxidase from SDS and added nucleotides by gel filtration of the SDS-stimulated solubilized membrane-cytosol mixtures through a Sephadex G-25 column. By utilizing this method, it was found that the presence of micromolar concentrations of nonhydrolyzable GTP analogues during activation by SDS results in a marked increase in the recovery of SDS-independent, NADPH-dependent O2(-)-producing activity in the excluded volume of the column. It is suggested that GTP stabilizes the SDS-induced complex between membrane and cytosolic components of the oxidase. Cell-free activation of NADPH oxidase by SDS was found to be cholera and pertussis toxin insensitive. These results serve as evidence of the participation of a G protein in the activation of the O2(-)-generating NADPH oxidase of macrophages by SDS.

Animals↗
PubMed1989

Activation of the superoxide-forming NADPH oxidase of macrophages requires two cytosolic components--one of them is also present in certain nonphagocytic cells.

The superoxide-forming NADPH oxidase of resting macrophages can be activated in a cell-free system by certain anionic amphiphiles, most notably SDS. Activation requires the cooperation of membrane-associated and cytosolic components. We now report that at least two cytosolic factors are required for SDS-elicited activation of NADPH oxidase of guinea pig macrophages. Treatment of cytosol with ammonium sulfate at 37% saturation led to the partition of the two factors in the supernatant and precipitate fractions (termed components sigma 1 and sigma 2, respectively). Although each fraction by itself was inactive, recombining them resulted in complete recovery of the original ability of native cytosol to support SDS-elicited superoxide production by octyl-glucoside solubilized macrophage membranes. Both components are proteins, as shown by their susceptibility to trypsin and proteinase K, and were inactivated by heating at 60 degrees C. sigma 2, but not sigma 1, was inactivated by treatment with the covalent sulfhydryl reagent N-ethylmaleimide. On high-performance gel filtration, sigma 1 was found to have a molecular mass of 30 to 52 kDa, whereas sigma 2 eluted with molecules of 150 to 440 kDa. Component sigma 1 was partially purified from the ammonium sulfate supernatant fraction of cytosol by hydrophobic interaction chromatography followed by gel filtration. A material behaving like sigma 1 was also found to be present in the cytosol of guinea pig thymus cells, lymph node lymphocytes and brain and of the mouse myeloma cell line MOPC 315. However, sigma 2 appears to be strictly phagocyte specific. The molecular characteristics of sigma 1 components from nonphagocytic cells were similar to those of macrophage sigma 1, as shown by their presence in the supernatant, after treatment of cytosol with ammonium sulfate at 37% saturation, a molecular mass close to 30 to 52 kDa and a similar behavior on hydrophobic interaction chromatography. These findings raise the possibility that cytosolic component sigma 1 might be the bearer of a cellular function, more general than the one suggested by its role in the activation of NADPH oxidase of phagocytes.

Ammonium Sulfate↗
PubMed1989

Activation of the superoxide forming NADPH oxidase in a cell-free system by sodium dodecyl sulfate. Absolute lipid dependence of the solubilized enzyme.

The superoxide (O2-)-forming NADPH oxidase of resting macrophages can be activated in a cell-free system by certain anionic amphiphiles, such as sodium dodecyl sulfate (SDS). O2- production requires the cooperation of membrane-associated and cytosolic components. The membrane component can be solubilized by octyl glucoside yielding a highly active oxidase preparation. High performance gel filtration of the solubilized oxidase on Superose 12 in the presence of 40 mM octyl glucoside leads to the total loss of enzymatic activity. This can be restored in previously inactive eluate fractions by "reconstitution" with N-ethylmaleimide or heat (60 degrees C)-inactivated total solubilized membrane. Oxidase activity, that becomes evident upon reconstitution, is eluted from Superose 12 with molecules in the Mr range of 300,000-71,000. The material with reconstitutive capacity is completely dissociated from the oxidase, eluting with molecules in the Mr range of 71,000-11,000. The Superose 12 elution profile of the material responsible for reconstitution coincides with that of membrane-derived phospholipid. Also, the reconstitutive capacity of total solubilized membrane and that of the Mr 71,000-11,000 region of the Superose eluate are recovered in a chloroform extract prepared by the method of Bligh and Dyer. It is concluded that loss of oxidase activity by gel filtration at a high octyl glucoside concentration is the consequence of delipidation. NADPH oxidase activity, revealed by reconstitution of Superose 12 fractions with exogenous phospholipid, correlates closely with the elution profile of cytochrome b559. Reconstitution of activity of delipidated oxidase can also be achieved with natural non-macrophage phospholipids and with synthetic phospholipids. Reconstitution of NADPH oxidase activity by lipids is governed by the following rules: (a) phospholipids are effective; lysophospholipids and neutral lipids are not; (b) phospholipids with polar heads represented by choline, ethanolamine, and serine, as well as cardiolipin, are effective; phosphatidylinositol is much less active; (c) phospholipids with unsaturated fatty acid residues are capable of reconstitution while saturated acyl residues do not confer activity; this specificity appears not to be related to the transition temperature of the phospholipids.

Ammonium Sulfate↗
PubMed1988

Certain lymphoid cells contain the membrane-associated component of the phagocyte-specific NADPH oxidase.

Anionic amphiphiles such as long chain unsaturated fatty acids and SDS were shown to activate the superoxide (O2-) producing NADPH oxidase in a cell-free system derived from sonically disrupted phagocytes (macrophages and granulocytes). O2- production required the cooperation of a membrane associated component sedimenting at 48,000 X g (pi) and a cytosolic factor (sigma). The purpose of the present investigation was to find out whether components pi and sigma were also present in non-phagocytic cells that do not produce O2- when stimulated. It was found that the 48,000 X g pellets of guinea pig lymph node and thymus cell sonicates contained significant amounts of component pi, as shown by their ability to support SDS-elicited NADPH-dependent O2- production when supplemented with macrophage cytosol. Lymph node and thymus pi could be extracted from the membrane by 30 mM octyl glucoside, just as its macrophage-derived equivalent. Combining lymph node and thymus 48,000 X g pellet with autologous cytosol did not yield an active enzyme preparation. Also, cytosol from lymph node and thymus cells could not cooperate with macrophage 48,000 X g pellet, indicating that component sigma was lacking in lymphoid cells. Neither pi nor sigma could be detected in guinea pig kidney, the mouse myeloma cell line MOPC 315 and the canine cell line Cf2Th. The 48,000 X g pellet of all nonphagocytic cells examined contained a b-cytochrome that resembled, by its spectral characteristics, the cytochrome b559 thought to be characteristic of phagocytes. In macrophages, cytochrome b559 represented 80% of b-cytochrome content of the 48,000 X g pellet, whereas in non-phagocytic cells, the equivalent material represented only 50 to 60%. There was no correlation between the presence and quantity of the cytochrome b559-like chromophore in the 48,000 X g pellet of a particular cell type and its ability to cooperate with macrophage cytosol in SDS-elicited O2- production.

Animals↗
PubMed1988

Macrophage-derived superoxide-generating NADPH oxidase in an amphiphile-activated, cell-free system; partial purification of the cytosolic component and evidence that it may contain the NADPH binding site.

The cytosolic component of macrophage-derived superoxide generating NADPH oxidase was partially purified by affinity chromatography on 2',5'-ADP-agarose. Elution was nonspecific by elevated phosphate molarity. A single step attains at least 40-fold enrichment of specific activity, the recovery being over 20%. Elution with various ligands in the concentration range 2-3.5 mM was also tested. The most effective ligands were: ATP, dATP, GTP, NADPH and 2',5'-ADP. Ineffective were AMP, 2'-AMP, FMN, FAD and NADH. ADP was of medium potency. On the basis of the above and other results, we infer that the molecule (or complex) purified by us may contain the enzymatic NADPH binding site. This component is fully retained by a 100 kDa cutoff membrane and is labile at room temperature, the lability being cancelled by 2-mercaptoethanol.

Animals↗
PubMed1987

Activation of the superoxide forming NADPH oxidase in a cell-free system by sodium dodecyl sulfate. Characterization of the membrane-associated component.

Sodium dodecyl sulfate (SDS) was shown to elicit NADPH-dependent superoxide (O2-) production by a cell-free system derived from sonically disrupted resting guinea pig macrophages (Bromberg, Y., and Pick, E. (1985) J. Biol. Chem. 260, 13539-13545). O2- production was absolutely dependent on the cooperation between a membrane-associated component, sedimenting with the 48,000 X g pellet and a cytosolic factor, nonsedimentable at 265,000 X g. The present report describes the solubilization and characterization of the membrane-associated component of the SDS-activable O2(-)-forming NADPH oxidase (operationally termed pi). Treatment of the 48,000 X g pellet with 30 mM octyl glucoside resulted in complete transfer of pi to the soluble fraction. The solubilized pellet produced an average of 0.92 mumol of O2-/mg of protein/min upon reduction of octyl glucoside content below the critical micellar concentration and in the presence of cytosol, 100 microM SDS, and 0.2 mM NADPH. The activity of solubilized pellet-cytosol combinations was also expressed as NADPH-dependent, azide-resistant oxygen consumption and hydrogen peroxide production. pi was inactivated by the sulfhydryl reagent p-chloromercuribenzoate. Solubilized pellet contained spectroscopically detectable cytochrome b559 (225.6 +/- 15.0 pmol/mg mg protein). Both pi and cytochrome b559 were bound by Cibacron Blue Sepharose and could be eluted by a gradient of octyl glucoside (0-30 mM) in the presence of 1 M KCl. On high performance gel filtration on Superose 12, both pi and cytochrome b559 eluted in the excluded volume; when 25 mM octyl glucoside was present in the elution buffer, pi was partially dissociated from cytochrome b559. Sequential purification of pi on Blue Sepharose followed by gel filtration on Superose 12 in the presence of 25 mM octyl glucoside lead to complete resolution of pi from cytochrome b559 (pi was found in the Mr = 28,000 - 11,000 range while the bulk of cytochrome b559 eluted in the Mr = 113,000 - 71,000 range). We propose that pi is distinct from cytochrome b559 and represents a membrane-associated component in an amphiphile-activated electron transport chain from NADPH to oxygen.

Animals↗
PubMed1986

Characterization of Ca2+-activated, phospholipid-dependent protein kinase C/protein kinase M in guinea pig peritoneal exudate macrophages.

Protein kinase C (C-kinase) is shown to be present in the cytosolic and particulate fractions of mineral oil induced peritoneal macrophages of guinea pigs. By omission or use of a high concentration of leupeptin, three forms of the enzyme were obtained: stimulant/Ca2+/phospholipid-dependent C-kinase, eluted from DEAE 52 cellulose at 0.08-0.16 M NaCl; stimulant/Ca2+/phospholipid-independent protein kinase M (M-kinase), and Ca2+-inhibited & stimulant/phospholipid-dependent form of protein kinase, both eluted from DEAE 52 cellulose at 0.18-0.22 M NaCl. Phorbol ester or 1,2-diacylglycerol were used as stimulants. It is suggested that Ca2+-inhibited & stimulant/phospholipid-dependent protein kinase represents the in vivo form of the M-kinase in intact cells.

Animals↗
PubMed1986

The mechanism of action of lymphokines. IX. The enzymatic basis of hydrogen peroxide production by lymphokine-activated macrophages.

The purpose of this study was to elucidate the biochemical basis of the enhanced hydrogen peroxide (H2O2) production by guinea pig peritoneal macrophages (MP) cultured in lymphokine (LK)-containing medium. The markedly augmented H2O2 generation by these cells, demonstrable by the horseradish peroxidase (HRP)-catalyzed oxidation of phenol red, is distinguished by its lack of dependence on a second stimulus. We demonstrate that H2O2 production is truly spontaneous and is not caused by a stimulant present among the H2O2 assay reagents. The principal candidate for such a role was HRP type II (a mixture of five isoenzymes) that was reported to be capable of eliciting an oxidative burst in MP. Four distinct HRP isoenzymes that were found incapable of provoking an oxidative response were nevertheless adequate for demonstrating H2O2 production by LK-activated MP. Blocking the MP receptor for mannose by the addition of mannan to the assay system resulted in enhanced detection of H2O2 by low concentrations of HRP type II and by three out of four HRP isoenzymes. Treatment of MP with LK-containing medium for 72 hr did not result in a significant change in the activity of cellular superoxide dismutase (SOD) compared with MP cultured for the same length of time in control medium. By using the specific inhibitor of copper, zinc-containing SOD, sodium diethyldithiocarbamate (DDC), and the universal SOD inhibitor, sodium nitroprusside, we found that the predominant enzyme in guinea pig peritoneal MP is probably manganese-containing SOD. Incubation of LK-activated MP with nitroprusside resulted in almost total inhibition of H2O2 production and a simultaneous switch to superoxide (O2-) liberation. Similar exposure to DDC had no effect. These data indicate that H2O2 produced by LK-activated MP is derived exclusively by enzymatic dismutation of O2- mediated by a manganese-containing SOD. The increase in spontaneous H2O2 production induced by LK is therefore secondary to augmented O2- production that occurs at a cellular location where O2- is accessible to SOD. The enzymatic basis of the enhanced oxygen radical production was investigated by determining the kinetic parameters of the O2- -forming NADPH oxidase of resting LK-treated MP in a cellfree system in which O-2 production was induced by sodium dodecyl sulfate. The Km for NADPH and the Vmax of the enzyme of LK-treated MP were not different from those of the enzyme of MP incubated in control medium. We conclude that LK treatment of MP does not modulate the NADPH oxidase itself but, most likely, a process related to activation of the enzyme.

Animals↗
PubMed1985

Activation of NADPH-dependent superoxide production in a cell-free system by sodium dodecyl sulfate.

Sodium dodecyl sulfate (SDS) elicits the production of superoxide (O2-) by a cell-free system represented by sonically disrupted guinea pig peritoneal macrophages. O2- generation requires NADPH and a heat-sensitive cellular component, is proportional to the amount of macrophage protein, and exhibits a pH optimum of 6.5-7. The kinetic parameters of the SDS-stimulated enzyme are: Km (+/- S.E.) = 0.0367 +/- 0.003 mM NADPH and Vmax (+/- S.E.) = 73.46 +/- 9.09 nmol O2-/mg of protein/min. O2- production is dependent on the cooperation between a particulate subcellular component sedimentable at 48,000 X g and a cytosolic factor present in the 48,000 X g supernatant. The activity of both components is destroyed by heating at 80 degrees C. Pretreatment of intact macrophages with phorbol myristate acetate results in the partial removal of the requirement for cytosolic factor; SDS is now capable of activating the isolated 48,000 X g pellet. Among a large number of anionic, cationic, and nonionic detergents tested, only the anionic detergents SDS and sodium dodecyl sulfonate are capable of eliciting O2- production in the cell-free system, SDS being the more potent stimulant. It is proposed that the structural requirements that make these compounds capable of activating the O2- forming NADPH oxidase in a cell-free system are the presence of an anionic polar head and a long hydrophobic alkyl tail. We suggest that sodium salts of long chain unsaturated fatty acids that were found by us to be capable of stimulating O2- production in a cell-free system (Bromberg, Y., and Pick, E. (1984) Cell. Immunol. 88, 213-221) owe their activity to the fact that they function as anionic detergents.

Animals↗
PubMed1985

The mechanism of action of lymphokines. VIII. Lymphokine-enhanced spontaneous hydrogen peroxide production by macrophages.

Oil-elicited guinea-pig peritoneal macrophages (MPs) cultured for 2-3 days in medium containing supernatant of concanavalin A-activated lymphocytes (lymphokine, LK) generated large amounts of hydrogen peroxide (H2O2), as detected by the horseradish peroxidase (HRP)-dependent oxidation of phenol red, in the absence of further stimulation. H2O2 production increased with the duration of exposure to LK and was evident at high dilutions of supernatant (1/64). Parallel cultures of MPs in medium or a supernatant of non-activated lymphocytes also increased their H2O2 production during culture but levels at all time intervals were significantly lower than those measured in LK treated cultures. The marked increase in H2O2 production was associated with only a moderate increment in superoxide (O-2) liberation and this was not specific for LK treated cells. Detection of LK-dependent H2O2 production was dependent on ongoing pinocytosis during the assay. This and other arguments suggest that the HRP-phenol red assay, as applied here, detects H2O2 generation occurring at the level of intracellular vesicles and it is concluded that LK elicits H2O2 production that is limited to the intracellular compartment. H2O2 is, apparently, derived by non-enzymatic dismutation of O-2 taking place within the cell; LK treatment of MPs also resulted in a significant reduction in catalase activity.

Animals↗