Primary stimuli of icosanoid release inhibit arachidonoyl-CoA synthetase and lysophospholipid acyltransferase. Mechanism of action of hydrogen peroxide and methyl mercury in platelets

Icosanoid formation in platelets depends on the concentration of free arachidonate that is mainly liberated from membrane phospholipids by phospholipase A2. The concentration of free arachidonate is also controlled by the activities of the reacylating enzymes arachidonoyl-CoA synthetase and lysophospholipid acyltransferase. In human platelet microsomes we determined the high enzyme activities of 5.9 nmol.min-1.(10(9) platelets)-1 for the arachidonoyl-CoA synthetase and 37 nmol.min-1.(10(9) platelets)-1 for the lysophospholipid acyltransferase. The activities of these reacylating enzymes were strongly reduced by hydrogen peroxide (H2O2) and methyl mercury that are primary stimuli of arachidonate release in intact platelets. H2O2 inhibited the arachidonoyl-CoA synthetase with an IC50 of 3.3 mmol/l without affecting the lysophospholipid acyltransferase. Sulfhydryl group protection by 3-mercapto-1,2-propanediol did not overcome the inhibition but glutathione prevented the inhibition of the arachidonoyl-CoA synthetase by H2O2. This suggests that glutathione by virtue of the glutathione peroxidase reduces H2O2 rather than that it protects free sulfhydryl groups of the arachidonoyl-CoA synthetase. Methyl mercury left the arachidonoyl-CoA synthetase activity unaffected but inhibited the lysophospholipid acyltransferase activity with an IC50 of 3.4 mumol/l. The inhibition is probably evoked by the blockade of sulfhydryl groups of the lysophospholipid acyltransferase because it disappeared when 3-mercapto-1,2-propanediol was added at a concentration higher than that of methyl mercury. Thrombin as a physiological full agonist, Ca2+ less than or equal to 1 mmol/l, the calcium ionophore A23187 and phorbol 12-myristate 13-acetate (TPA) and 1-oleoyl-2-acetylglycerol as model stimuli of protein kinase C neither influenced arachidonoyl-CoA synthetase nor lysophospholipid acyltransferase. It is concluded that the inhibitory effect of H2O2 and methyl mercury on the arachidonate-reacylating enzymes arachidonoyl-CoA synthetase or lysophospholipid acyltransferase, respectively, are responsible for their capacity to stimulate icosanoid release in intact cells. Thrombin and its intracellular messengers Ca2+ and diacylglycerol do not directly affect arachidonoyl-CoA synthetase and lysophospholipid acyltransferase.

Embryonic mortality attributed to inherited deficiency of uridine monophosphate synthase

The deficiency of uridine-5'-monophosphate synthase is inherited as an autosomal recessive trait in Holstein-Friesian cattle. Heterozygotes are characterized by half normal activity of uridine monophosphate synthase, as measured in erythrocytes. Matings between heterozygotes for the deficiency have produced 31 pregnancies lasting at least one month, but only 23 full-term calves, including 9 homozygous normal and 14 heterozygotes. That the eight embryos were not carried to term is consistent with the probability of a homozygous-deficient genotype and are lost around 40 d of gestation. Although the homozygous deficiency of uridine monophosphate synthase is lethal embryonically in cattle, homozygotes for the analogous human condition have been born alive.

High-molecular-mass proteinases in rabbit reticulocytes: the multicatalytic proteinase is an ATP-independent enzyme and ATP-activated proteolysis is in part associated with a cysteine proteinase complexed to alpha 1-macroglobulin

We have investigated the proteolytic degradation of [14C]methylcasein and 125I-labeled bovine serum albumin at pH 7.8 and 37 degrees C by lysates of rabbit reticulocytes purified from rabbit blood by two different procedures. (I) Lysates obtained from reticulocytes after removal of plasma and buffy coat as well as after washing of cells, degraded casein and albumin, and released from the two substrates 1.3%/h and 0.4%/h, respectively, of acid-soluble radioactivity. The activity towards both substrates was stimulated about 4-fold by ATP/Mg2+. Chromatography of whole blood on a column of cellulose prior to washing and lysis of cells had profound but differential effects on these activities in that stimulation of casein-degradation by ATP/Mg2+ was almost completely lost, whereas degradation of albumin, albeit at a low rate, was measurable in the presence of ATP/Mg2+ only. (II) Degradation of casein by these lysates is largely inhibited by a monospecific antibody against rabbit multicatalytic proteinase, whereas digestion of albumin is not affected by the antibody, either in the presence or absence of ATP/Mg2+. The latter activity is partially inhibited by a specific antibody against rabbit alpha 1-macroglobulin. (III) The immunoreactive amount of multicatalytic proteinase is about 1.2 micrograms per mg of lysate protein and almost identical in the two lysates. In contrast, the immunologically detectable levels of alpha 1-macroglobulin vary and are much lower in reticulocyte-lysates following chromatography on cellulose than in lysates from washed reticulocytes. (IV) Caseinolytic activity of multicatalytic proteinase, purified from rabbit reticulocyte lysate, is not activated by ATP/Mg2+ and the enzyme is proteolytically inactive towards albumin. On the other hand, a complex consisting of the proteinase inhibitor alpha 1-macroglobulin and the cysteine proteinase, cathepsin B, does degrade both substrates at pH 7.8, in an ATP/Mg2+-activated fashion. From these results it is concluded that the multicatalytic proteinase is an ATP-independent enzyme and a cellular constituent of rabbit reticulocytes whereas the activity stimulated by ATP/Mg2+ appears to be associated, at least in part, with a cysteine proteinase complexed to alpha 1-macroglobulin.

Inhibition and complexation of activated protein C by two major inhibitors in plasma

To determine the major physiologic inhibitors of activated protein C (APC), plasma was incubated with APC or with Protac C and subjected to immunoblotting. APC:inhibitor complexes gave two major bands reacting with antiprotein C antibodies when immunoblotted on nondenaturing gels, and additional minor bands that varied between serum and plasma. Formation of one of the two major bands of APC:inhibitor complex, but not the other, was stimulated by heparin and only this band reacted with antibodies to the previously described APC inhibitor that is here designated PCI-1. Plasma immunodepleted of PCI-1 formed complexes with APC as visualized with antiprotein C but not anti-PCI-1 antibodies, and exhibited heparin-independent inhibition of APC activity, providing evidence for the existence of a second major physiologic APC inhibitor, PCI-2. Formation of APC:PCI-2 complexes in PCI-1-depleted plasma paralleled inhibition of APC amidolytic activity. PCI-2 was separated from PCI-1 and partially purified using column chromatography. PCI-2 formed inactive complexes of approximately 110,000 molecular weight (mol wt) with APC suggesting PCI-2 has an approximate mol wt of 50,000. Thus, inhibition of APC in plasma involves two major distinct 50,000 mol wt inhibitors, the heparin-dependent PCI-1 and the heparin-independent PCI-2.

Activation and complexation of protein C and cleavage and decrease of protein S in plasma of patients with intravascular coagulation

Activated protein C (APC) is inhibited by two major plasma inhibitors (PCIs). To find evidence for in vivo complexation of APC, immunoblotting studies were performed on plasmas of 85 patients with suspected disseminated intravascular coagulation (DIC). Samples from 62 of these patients contained 5% to 35% of protein C antigen in APC:inhibitor complexes, indicating that protein C activation and inhibition had occurred. In 24 normal plasmas, no detectable APC:PCI complexes were observed (less than 5%). Patients with higher levels of complexes had more abnormal coagulation test data for DIC. The major band of APC complexes detected by anti-protein C antibodies did not react with antibodies to the heparin-dependent protein C inhibitor (PCI-1) previously described. Rather, APC was complexed with another recently described plasma protein C inhibitor, PCI-2. Immunoblotting studies for protein S, the cofactor for APC, revealed that the majority of the DIC patient plasmas contained a higher than normal proportion of protein S in cleaved form, suggesting that protein S may have been proteolytically inactivated. Protein S total antigen levels were also found to be low in DIC patients, excluding those with malignancy. These studies support the hypothesis that the protein C pathway is activated during DIC.

Formation of C1s-C1-inhibitor, kallikrein-C1-inhibitor, and plasmin-alpha 2-plasmin-inhibitor complexes during cardiopulmonary bypass

Stimulation of platelets and neutrophils occurs during clinical cardiopulmonary bypass. We investigated whether the classical complement, contact, or fibrinolytic pathways are activated as potential sources of neutrophil agonists. Using enzyme-linked immunosorbent "sandwich" assays specific for C1s-C1-and kallikrein-C1-inhibitor complexes respectively, we found that there was a modest increase in plasma levels of each complex after clinical cardiopulmonary bypass was completed. The increased concentration of enzyme-inhibitor complexes reverted to baseline within 24 hours. Since these complexes are cleared in vivo, we measured their formation by assaying their plasma levels during in vitro simulated extracorporeal circulation. Over a period of two hours, C1s-C1-inhibitor complexes rose from a baseline of 2 +/- 1 nmol/L to 21 +/- 2 nmol/L, and kallikrein-C1-inhibitor complexes rose from 2 +/- 1 nmol/L to 25 +/- 5 nmol/L. However, there was no evidence of either in vivo or in vitro plasmin-alpha 2-plasmin-inhibitor complex formation. These results indicate that the pathways of classical complement and contact activation, but probably not fibrinolysis, may be associated with neutrophil activation seen during clinical cardiopulmonary bypass.

Macroxyproteinase (M.O.P.): a 670 kDa proteinase complex that degrades oxidatively denatured proteins in red blood cells

Erythrocytes and reticulocytes are shown to undergo rapid rates of protein degradation following exposure to oxidative stress. Experiments with ATP depletion revealed that, unlike the proteolysis of many other abnormal proteins, the degradation of oxidatively modified proteins is an ATP-independent process. Ion exchange chromatography (DEAE Sepharose CL-6B), ammonium sulfate precipitation, gel filtration chromatography (Sephacryl S-300 or Sepharose CL-6B), and a second ion exchange step were used to resolve the activity responsible for degrading oxidatively modified proteins from (dialyzed) cell-free extracts of erythrocytes and reticulocytes. Gel filtration studies revealed that some 70-80% of the activity in erythrocytes, and some 60-70% of the activity in reticulocytes, is expressed by a 670 kDa proteinase complex that is not stimulated by ATP (in fact, ATP is slightly inhibitory). This proteinase complex is inhibited by sulfhydryl reagents, serine reagents, and transition metal chelators, and has a pH optimum of 7.8. We propose the trivial name "macroxyproteinase" or "M.O.P." (abbreviated from Macro-Oxy-Proteinase) for the complex because of its large size, substrate preference (oxidatively modified proteins), and inhibitor profile (which indicates multiple catalytic sites). Electrophoresis studies of the 670 kDa M.O.P. complex revealed the presence of 8 distinct polypeptide subunits with the following apparent molecular sizes: 21.5, 25.3, 26.2, 28.1, 30.0, 31.9, 33.3, and 35.7 kDa. The large molecular size of the M.O.P. complex, its ATP- and ubiquitin-independence, its inhibitor profile, its distinctive subunit banding pattern in denaturing electrophoresis gels, its pH optimum, and its proteolytic profile with fluorogenic peptide substrates all indicate that M.O.P. is identical to 600-700 kDa neutral/alkaline proteinase complexes that have been isolated from a wide variety of eucaryotic cells and tissues, but for which no function has previously been clear. We propose that macroxyproteinase is responsible for catalyzing most of the selective degradation of oxidatively denatured proteins in red blood cells. We further suggest that M.O.P. may perform the same function in other eucaryotic cells and tissues.

Ca2+ effect on ATP-independent lysophospholipid transacylases is indissociable from Ca2+ effect on phospholipase A2 activity in rat platelet sonicates

CoA-dependent transacylation and phospholipid hydrolysis were studied in parallel experiments using rat platelet sonicates. The decrease observed in palmitoyllyso-sn-glycero-3-phosphocholine (palmitoyllyso-GPC) transcylation as a function of Ca2+ concentration was found to be correlated with appearance of endogenous lysoderivatives. We also demonstrated that endogenously produced acyllyso-sn-glycero-3-phosphoethanolamine (acyllyso-GPE) induced CoA-dependent arachidonate transfer from diacyl-GPC. These results further argue for a two-step arachidonate release from diacyl-GPC when platelets are stimulated with thrombin.

Assessment of effects of amino acids and branched chain keto acids on leucine oxidation in human lymphocytes

Effects of amino acids and branched chain keto acids on leucine transamination and oxidation were assessed in peripheral human lymphocytes. Isoleucine (80-200 mumol/l) and valine (250-500 mumol/l) diminished transamination and oxidation of leucine up to 25%, glutamine (50-1000 mumol/l) up to 55%. alpha-Ketoisocaproic acid (KIC; 200 mumol/l) augmented the activity state of branched chain keto acid dehydrogenase by 40%. It is concluded that in peripheral human lymphocytes (1) isoleucine, valine and glutamine are physiological inhibitors of leucine catabolism, and (2) leucine can promote its own degradation via KIC.

Tetrahydrobiopterin deficiency: assay for 6-pyruvoyl-tetrahydropterin synthase activity in erythrocytes, and detection of patients and heterozygous carriers

6-Pyruvoyl-tetrahydropterin synthase (PTS), a key enzyme in the synthesis of tetrahydrobiopterin in man, is defective in the most frequent variant of tetrahydrobiopterin-deficient hyperphenylalaninaemia (atypical phenylketonuria). An assay for PTS activity in erythrocytes was developed. It is based on the PTS-catalysed formation of tetrahydrobiopterin from dihydroneopterin triphosphate in the presence of magnesium, sepiapterin reductase, NADPH, dihydropteridine reductase, and NADH, and fluorimetric measurement of the product as biopterin by high performance liquid chromatography (HPLC) after oxidation with iodine. The PTS activity was higher in younger erythrocytes, including reticulocytes, than in older ones. Fetal erythrocytes showed approx. four times higher activities than those of adults. Using a more purified human liver sepiapterin reductase fraction which gave a lower yield than a crude preparation, adult controls (n = 8) showed a mean erythrocyte PTS activity of 17.6 (range 11.0-29.5) microU/g Hb. Nine of 11 patients with typical PTS deficiency showed activities between 0% and 8% of the mean of controls, and two of 11 showed 14% and 20%, respectively. The obligate heterozygotes (n = 16) had activities of 19% (range 8%-31%) of the mean of controls, i.e., significantly less than the expected 50%. Four patients with the "peripheral" type of the disease showed 7%-10% of the mean of controls. Thus, the assay did not distinguish between patients and heterozygotes in every family. The assay is well suited to the identification of heterozygotes of PTS deficiency in family studies.

Oxidation of leucine in human lymphocytes

Appropriate conditions for analysis of leucine oxidation in peripheral human lymphocytes were determined. Lymphocytes, isolated by Ficoll centrifugation, were washed in phosphate-buffered saline without additions, with 5 mmol/l ADP or with 5 mmol/l ADP plus 25 mmol/l NaF for determination of transaminase activity, and total and basal activity of branched chain keto acid dehydrogenase (BCKA-D), respectively. Cells were incubated for 20-60 min with [1-14C]-leucine, or [1-14C]-alpha-ketoisocaproic acid (KIC) in the presence of various concentrations of the respective unlabelled substrates. Pyridoxal phosphate (0.1 mmol/l) augmented transaminase activity, coenzyme A, NAD and thiaminepyrophosphate (0.5 mmol/l each) enhanced BCKA-D activity. Apparent Km values for transamination and for BCKA-D were 40 and 17 microM, respectively. Total capacity for leucine transamination was about five times greater than for oxidation of KIC. The mean activity state of BCKA-D was 30%. Oxidation of KIC declined when 5.6 mmol/l glucose was added to the medium. It is concluded that: (1) BCKA-D is rate-limiting for leucine catabolism in peripheral human lymphocytes, (2) the BCKA-D complex is normally only partially active, and (3) flux of leucine through BCKA-D is inhibited by physiological glucose concentrations.

Characterization of UMP synthase in dairy cattle heterozygous for a lethal recessive trait

UMP synthase was characterized biochemically in dairy cattle heterozygous for a deficiency of this enzyme. Both activities comprising this bifunctional enzyme are decreased, with OMP decarboxylase more affected than orotate phosphoribosyltransferase. Immunotitration of UMP synthase activity revealed the presence of the protein product of the mutant allele in the heterozygous animals. UMP synthases from normal and deficient cattle were not distinguished from one another by kinetic constants, responses to inhibitors, pH profiles, or thermal lability. It was concluded that the 50% reduction in enzyme activity in heterozygous cattle is the result of the presence of only half the normal level of catalytically active UMP synthase.

Comparative study on the stimulation of superoxide production in guinea-pig eosinophils by the calcium ionophore A23187

The effect of calcium and/or magnesium on O2- production by guinea-pig eosinophils stimulated by the calcium ionophore A23187 was studied in comparison to neutrophils. In the absence of calcium, A23187 did not stimulate O2- production in resting eosinophils and neutrophils, regardless of the presence of extracellular magnesium. The A23187-induced O2- production by both cells increased linearly with extracellular Ca2+ concentrations. However, the concentration of Ca2+ required for maximum O2- production in eosinophils was about 10-times lower than that required of neutrophils. The addition of Mg2+ strongly inhibited O2- production, especially in eosinophils at low Ca2+ concentrations. The intracellular Ca2+ concentration was lower in eosinophils than in neutrophils in the resting state, and the enhancement of the intracellular Ca2+ concentration in response to A23187 was much lower in eosinophils than in neutrophils. The activation of the NADPH-dependent O2(-)-forming enzyme (NADPH oxidase) in eosinophils depended on extracellular calcium, as observed in O2- production. However, the NADPH oxidase activity in the particulate fraction from A23187-stimulated eosinophils was only slightly affected by the addition of divalent cations or EDTA. The compound W-7 (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride), a calmodulin antagonist, significantly inhibited O2- production by both cells. On the other hand, the compound H-7 (1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride), a protein kinase C antagonist, was less effective on O2- production than was W-7. H-7 had little effect on O2- production of eosinophils. These findings suggest that NADPH oxidase might be activated by a smaller Ca2+ concentration through the calmodulin-dependent reaction. This was not observed with protein kinase C, at least in eosinophils.

A new inherited variant of the 3 beta-hydroxysteroid dehydrogenase-isomerase deficiency syndrome: evidence for the existence of two isoenzymes

The clinical and endocrine features of a unique form of adrenal insufficiency secondary to an inherited deficiency of 3 beta-hydroxysteroid dehydrogenase-isomerase (3-HSD) were studied. The propositus was a 19-yr-old man with a history of repeated episodes of acute adrenal crisis. Family study disclosed that a 6-yr-old female sibling also was affected, and a third sibling had died during the course of an adrenal crisis. The diagnosis of adrenal insufficiency was established on the basis of extremely low serum cortisol levels and urinary 17-hydroxycorticosteroid excretion with concomitantly elevated serum ACTH levels and lack of cortisol response to ACTH administration. Impairment of C-21 steroid 3-HSD activity was strongly suggested by persistency elevated serum 17-hydroxypregnenolone to 17-hydroxyprogesterone and pregnenolone to progesterone ratios, their significant increase after ACTH administration, and their return to normal during cortisol therapy in both patients. Nevertheless, the serum dehydroepiandrosterone to androstenedione ratio, both basally and after ACTH and/or hCG stimulation, was normal. These findings coupled with the normal phenotypic development and onset of puberty in the two patients indicated intact C-19 steroid 3-HSD activity. The overall results indicate an inherited impairment of 3-HSD activity confined only to C-21 steroid substrates and, thus, suggest the existence of at least two 3-HSD isoenzymes under independent genetic regulation.

[Kinetic model of a multienzyme system of blood prostanoid synthesis. I. Mechanism of stabilization of thromboxane and prostacyclin levels]

A kinetic scheme of the prostacyclin-thromboxane system has been evolved on the basis of the authors experimental data and the results described elsewhere. The kinetic behavior of the model has been analysed with the aid of computer technology by varying the following parameters: phospholipase activities, free arachidonic acid exchange rates between platelets and endothelium, PGH-synthetase biosynthesis rates, velocities of arachidonic acid pathways other than the cyclooxygenase ones. It has been demonstrated that the biological system is capable of sustaining prostacyclin and thromboxane concentrations at steady fixed levels within a wide range of kinetic parameters.

[Kinetic model of a multienzyme system of blood prostanoid synthesis. II. Dynamic responses to pharmacological agents--inhibitors of prostaglandin H synthetases]

The dynamic replies of the multienzyme system of blood prostanoid synthesis to the introduction of an irreversible inhibitor of prostaglandin H synthetase (PGH synthetase) have been analysed by using kinetic modelling. The alterations of arachidonic acid and PGH synthetase concentrations in platelets and endothelium and the concentrations of thromboxane and prostacyclin have been demonstrated. Particularities of kinetic behaviour of the system probably providing the therapeutic effect of non-steroidal anti-inflammatory drugs have been shown. Namely, the kinetic wave of free arachidonic acid and prostacyclin concentration with respect to thromboxane concentration appears after introduction of the drugs.

Reticulocyte lipoxygenase, ingensin, and ATP-dependent proteolysis

Lipoxygenase purified from rabbit reticulocyte lysate has a molecular mass of 68 kDa on SDS gel and a pI of 5.97. Lipoxygenase is inhibited by nordihydroguaiaretic acid (NDGA), 3-amino-1-(m-(trifluoromethyl)phenyl)-2-pyrazoline (BW755C), 5,8,11,14-eicosatetraynoic acid (ETYA), salicylhydroxamate (SHAM) or hemin. Metal ions or nucleotides do not affect its activity. The addition of certain of these inhibitors to the reticulocyte extract also inhibited the ATP-dependent proteolysis of casein, one of the distinct characteristics of reticulocytes. No clear correlation between lipoxygenase activity and ATP-dependent proteolysis could be detected. Hemin and NDGA inhibited both processes, but the concentrations necessary for inhibition were quite different. SHAM completely inhibited lipoxygenase, but not proteolysis. o-Phenanthroline inhibited ATP-dependent proteolysis, but had no effect on lipoxygenase activity. We have also purified a high-molecular-mass protease, ingensin, from reticulocyte extract. This protease accounted for more than 90% of the casein-degrading activity in reticulocyte extract. NDGA inhibited ingensin at the same concentrations required for inhibition of ATP-dependent proteolysis. These results suggest that lipoxygenase is not indispensable for the ATP-dependent proteolysis and the novel high-molecular-mass protease, ingensin, may be involved in the process.

Effect of insulin on low-density-lipoprotein metabolism in human lymphocytes in vitro

The metabolism of low-density lipoproteins (LDL) in vitro in the presence of insulin was studied in freshly isolated human peripheral-blood lymphocytes. Insulin appeared to decrease the binding affinity of 125I-LDL to its cell-surface receptor, without any change in apparent Vmax or in the number of LDL receptors. As a consequence, the absolute amounts of 125I-LDL internalized and degraded were lower in the presence of insulin than in its abscence, although the fraction of internalized 125I-LDL degraded in either instance was quite similar. 3-Hydroxy-3-methylglutaryl-CoA reductase activity, and hence cholesterol synthesis, were stimulated by insulin. This effect of insulin was independent of the inhibitory effect of LDL on cholesterol synthesis. At the same time, acid cholesterol esterase and acyl-CoA: cholesterol O-acetyltransferase activities were lower in cells incubated with insulin than in controls. The net effect of these metabolic alterations seems to be that cells accumulate greater quantities of free and esterified cholesterol when treated with insulin.

Influence of age, sex, lactational state and exogenous growth hormone on erythrocyte UMP synthase in dairy cattle

UMP synthase activity was determined in erythrocytes of Holstein cattle to assess differences attributable to age, sex, lactational state, and exogenous growth hormone. Newborns had 80% more UMP synthase activity per ml erythrocytes than mature cattle. Males had 10% more UMP synthase activity than females of the same age. Lactating and non-lactating mature females did not differ in UMP synthase activity. Over the first six weeks of life, the decrease in UMP synthase activity was less pronounced in calves partially deficient for the enzyme. Ten daily injections of growth hormone altered neither UMP synthase activity in erythrocytes nor orotic acid concentrations in milk and urine.

Kinetic behavior of the multienzyme system of blood prostanoid synthesis

A kinetic scheme of the prostacyclin-thromboxane system has been evolved on the basis of our own experimental material and the results described elsewhere. The kinetic behavior of the model has been analysed with the aid of computer technology by varying the following parameters: phospholipase activities, free arachidonic acid exchange rates between platelets and endothelium, prostaglandin H (PGH) synthetase biosynthesis rates, velocities of arachidonic acid pathways other than cyclooxygenase ones. It has been demonstrated that the biological system is capable of sustaining prostacyclin and thromboxane concentrations at steady fixed levels within a wide range of kinetic parameters.

Studies of pyridine nucleotide oxidizing enzymes from human neutrophils

An NADH cytochrome c reductase has been identified in plasma membrane fractions from neutrophils in addition to the superoxide producing NADPH oxidase which has been extensively studied by other investigators. Activation of neutrophils resulted in increased enzyme activities but to different degrees; the NADH cytochrome c reductase increased 2 fold in specific activity and the NADPH oxidase 30 fold. Treatment of the plasma membrane fraction with sonication and differential centrifugation yielded a particulate fraction (R2) with a 2 fold increase in specific activities of both enzymes and concentrations of cytochrome b and FAD. The cytochrome b in the preparation was not reduced under anaerobic conditions by either NADH or NADPH. Treatment of preparations of R2 with deoxycholate or potassium thiocyanate separated the two enzymes yielding particulate preparations with only NADPH oxidase or NADH cytochrome c reductase activity, respectively.