Involvement of protein kinase A in the induction of arginase in murine bone marrow-derived macrophages

Arginase is induced in bone marrow-derived macrophages by agents that increase the intracellular concentrations of cAMP (Br-cAMP, prostaglandin E2) and, in their presence, the LPS induced NO synthesis is down regulated. Moreover, interleukin 10 which induces arginase in macrophages is able to increase the cAMP-dependent protein kinase A activity. In contrast, suppressors of NOS synthesis like protein kinase C inhibitors and calmodulin antagonists (W7), or NO activators (A23187) have no effect on the induction of arginase by LPS. These results strongly suggest that PKA is involved in the induction of arginase and supports the hypothesis that there is a reciprocal regulation of these two enzymes that drives the macrophages towards opposite functional states.

Oxidation of N(G)-hydroxyl-L-arginine to nitric oxide mediated by respiratory burst: an alternative pathway to NO synthesis

N(G)-Hydroxy-L-arginine is an intermediate metabolite in the synthesis of nitric oxide that is upregulated and secreted during acute inflammation in vivo. Previous reports have shown that chemically induced superoxide anion oxidizes N(G)-hydroxy-L-arginine to nitric oxide. Here, we demonstrate that this reaction takes place physiologically in phagocytic cells during the respiratory burst, and is independent of the presence of nitric oxide synthase.

Anti-MHV3 state induced by IFN gamma in macrophages is not related to arginine metabolism

In contrast to BALB/c mouse macrophages, the A/J macrophages after activation by interferon gamma (IFN gamma) develop an anti-MHV3 effect which correlates with the resistance to virus infection. To understand the cellular basis of this antiviral effect, we studied the possible involvement of arginine metabolism through nitric oxide (NO) and arginase induction, since these metabolic pathways have been described as implicated in antiviral activities of macrophages. The studies were performed by activating macrophages with inducers of NO (IFN gamma) and arginase (IL4 IL10). NO synthase (iNOS) and arginase inhibitors (N-methyl-arginine, NMA, and hydroxyarginine, OH-ARG) were used. The results show that in both macrophage populations, no spontaneous synthesis of NO occurred and the MHV3 enhanced the NO release induced by IFN gamma. After activation with IFN gamma, BALB/c macrophages released higher amounts of NO than the A/J macrophages. The inhibition of IFN gamma-induced NO-synthesis with NMA or with arginine free medium did not affect the virus replication. In BALB/c macrophages, IL4 or IL10, induced higher amounts of arginase than in A/J macrophages. In both macrophage populations the MHV3 infection had no influence on the arginase synthesized, and the inhibition of the arginase with OH-ARG had no influence on the virus growth. The level of MHV3 replication or inhibition was also not influenced when we used macrophages from knockout mice for the iNOS gene, and as a consequence were unable of synthesizing NO. These data indicate that NO and arginase do not participate in the anti-MHV3 state induced by IFN gamma in macrophages.

Reciprocal regulation of the nitric oxide synthase/arginase balance in mouse bone marrow-derived macrophages by TH1 and TH2 cytokines

Activation with lipopolysaccharide induces macrophages to produce the enzymes arginase and nitric oxide (NO) synthase. Both enzymes use as a substrate the amino acid L-arginine, which can be either hydrolyzed by arginase to urea and ornithine or oxidized by NO synthase to NO and citrulline. NO is important in the bactericidal and cytotoxic activities of macrophages. An equivalent functional role of arginase and its products is not known. We tested the induction of arginase in bone marrow-derived macrophages by endogenous mediators that are known to induce NO synthase, such as interferon-gamma (IFN-gamma), or suppress the induction of this enzyme, such as interleukin (IL)-4, IL-10, and prostaglandin E2 (PGE2). We find that PGE2 and the TH2 cytokines IL-4 and IL-10 are potent inducers of arginase. In contrast, the TH1 cytokine IFN-gamma does not induce arginase. Simultaneous application of both types of mediators leads to reduced induction of both arginase and NO synthase. Exposure of macrophage cultures to inducers of NO synthase exhausts their ability to respond subsequently to inducers of arginase. Conversely, exposure of the cells to inducers of arginase exhausts their ability to respond subsequently to inducers of NO synthase. The results are consistent with a competition of both enzymes for their substrate, L-arginine, with a reciprocal inhibition in the induction of both enzymes, or a combination of both phenomena. The enzymes NO synthase and arginase appear to define two alternate functional states of macrophages, induced by TH1 and TH2 cytokines, respectively.

Arginase induction by suppressors of nitric oxide synthesis (IL-4, IL-10 and PGE2) in murine bone-marrow-derived macrophages

The present study addresses the regulatory mechanisms involved in the arginine metabolism of macrophages by arginase and nitric oxide synthase. Induction of both enzymes with LPS or by mixed lymphocyte reaction has been reported. Here, we demonstrate that these enzymes can be independently induced in murine bone-marrow-derived macrophages with the appropriate agonists. Arginase expression is specifically triggered by IL-4, IL-10, PGE2 as well as non-toxic or detoxified LPS. Conversely, IFN gamma induces only NO synthesis in these cells. The results demonstrate that the metabolism of arginine in macrophages is controlled by TH1/TH2-dependent cytokines and suggest a regulatory role of arginase on the NO synthesis by intracellular substrate depletion.

Determination of arginase activity in macrophages: a micromethod

We propose a modification of Schimke's method for urea determination as a valuable micromethod for measuring arginase in activated macrophages. The method exhibits the following advantages: (a) it uses small amounts of samples (approximately 25,000 macrophages per assay); (b) it does not interfere with other related metabolites that are also present in the activated macrophage such as citrulline or arginine; (c) saturating concentrations of the substrate arginine can be used; and (d) it is much more sensitive than Schimke's method and can detect small amounts of urea, in the order of 0.02 mumol.

Oscillations in rat liver cytosolic enzyme activities of the urea cycle

Diurnal rhythms were studied in three rat liver enzymes of the urea cycle: arginase, arginosuccinate synthetase and arginosuccinase. In animals synchronized to a 12:12 h light-dark cycle these enzymes were determined at 8 different time points under three different feeding schedules: 24 h of fasting, ad libitum feeding and restricted feeding. Under the three experimental conditions maxima of enzyme activities occurred during the dark period. In all cases the maximum activity of arginosuccinase preceded the one of arginase and these in turn the one of arginosuccinate synthetase. On the other hand, the hepatic protein level was maximal during the light period and decreased to its lowest level during the dark period. The restriction of food between 08.00 h and 14.00 h induced an important phase shift of hepatic protein rhythm and arginosuccinase activity. Our results suggest that the diurnal rhythms of cytosolic enzymes of the urea cycle are not only dependent on the light-dark cycle, but also on the synchronizing and masking effect of food intake.

Kinetics and inhibition by some aminoacids of lactating rat mammary gland arginase

Some kinetic and regulatory properties of lactating rat mammary gland arginase were studied. At pH 7.4, i.e. at near-physiological conditions, there was evidence of inhibition by excess of substrate, with a Km value of 9.5 mM, slightly lower than the value of 18 mM observed at pH 9.8 (maximum enzyme activity). A study was also made of the effects of proline, ornithine, lysine and certain branched-chain aminoacids on enzyme activity: lactating rat mammary gland arginase was strongly and competitively inhibited by lysine, ornithine and valine, with Ki values of 1.2 mM, 1.1 mM and 3.6 mM, respectively. Other aminoacids (proline, isoleucine and leucine) also inhibited lactating rat mammary gland arginase, although to a lesser extent.

Immunological identity of the two different molecular mass constitutive subunits of liver arginase

A detailed understanding of the regulatory mechanisms of arginase in the cell will depend on the clarification of the origin of the two different molecular mass subunits and on the arrangements of them to constitute the native enzyme. Here, we show the immunological recognition of the 39.5 and 37.0 kDa subunits of arginase by antibodies against both subunits. We also find that the subunit stoichiometry (39.5 kDa: 37.0 kDa) present in purified arginase preparations as well as in fresh isolated microsomes and cytoplasm corresponds to 3:1, indicating high prevalence of a constant arrangement of the constitutive subunits of arginase. These findings represent evidence for a limited posttranscriptional or posttranslational modification of only a fraction of the synthesized arginase in liver.

Kinetics of manganese reconstitution and thiol group exposition in dialyzed rat mammary gland arginase

1. Rat mammary gland arginase is a metallo-enzyme dependent on Mn2+, which can be only partially substituted by Cd2+. 2. Reconstitution of the activity of dialyzed arginase by manganese is a two-phase process; the second phase is independent of the cation concentration, with a half-time recovery (t1/2) of 10.77 min. 3. The apparent Km for Mn2+ is 280 microM and 10.5 microM for enzyme dialyzed for 24 and 72 hr, respectively. 4. Treatment with 5 mM EDTA at pH 6 totally inhibits enzyme activity, which is reconstituted by Mn2+. 5. Results obtained with iodoacetamide treatment suggest the existence of sulphydryl groups accessible only when the enzyme is dialyzed.

Parallel induction of nitric oxide and glucose-6-phosphate dehydrogenase in activated bone marrow derived macrophages

The production of nitric oxide (NO.) and the induction of glucose-6-phosphate dehydrogenase by lipopolysaccharides (LPS) from different sources was studied in bone marrow derived macrophages (BMM phi). NO. production was found to be linked to the induction of glucose-6-phosphate dehydrogenase, suggesting the possible involvement of this enzyme in the cytotoxic mechanism resulting from the release of NO. by activated macrophages.

Preparation of activated supports containing low pK amino groups. A new tool for protein immobilization via the carboxyl coupling method

A method for the preparation of new aminated agarose gels containing monoaminoethyl-N-aminoethyl structures, MANA-agarose gels, has been developed. These gels contain primary amino groups with a very low pK value (6.8). In addition to that, we have been able to prepare very highly activated gels (e.g., 10% agarose gels containing up to 200 mu Eq of primary amines per milliliter). These two properties make these activated supports suitable for performing novel and interesting methods for protein immobilizations via very mild carbodiimide activation of carboxy groups. For example, very effective coupling reactions can be performed at pH 5.0-6.0 in the presence of low concentrations of activating agent, e.g., 1 mM. By using a model industrial enzyme, beta-galactosidase from Aspergillus oryzae, we have been able to demonstrate the excellent prospects of these novel activated supports.

Trypsin digestion of arginase: evidence for a stable conformation manganese directed

1. Controlled tryptic digestion of native arginase from rat liver suggests that Mn2+ promotes a stable conformation as shown by the following features. 2. An 18-fold increase in the half-life of arginase activity in the presence of Mn2+ is produced. 3. The stability of subunit B of arginase is increased in the presence of Mn2+ as revealed by SDS-PAGE during the time-course of trypsin cleavage. 4. The different digestion products of arginase with and without Mn2+ appearing during the time-course of tryptic treatment. 5. Different activity/bands protein ratio at any time of the tryptic digestion in the incubation mixtures, with and without Mn2+, are apparent.

Unfolding and trypsin inactivation studies reveal a conformation drift of glucose-6-phosphate dehydrogenase upon binding of NADP

Binding of NADP to glucose-6-phosphate dehydrogenase (G6PD) from Dicentrarchus labrax liver has stabilized its native structure against thermal inactivation, guanidine hydrochloride unfolding and inactivation by tryptic digestion. The time-course of G6PD inactivation by guanidine hydrochloride in the presence of NADP has provided experimental evidence in favor of a conformational drift upon NADP binding to the bass enzyme. Based on the inactivation patterns obtained when the enzyme was treated with guanidine hydrochloride and trypsin, it is proposed that the enzyme conformation induced upon NADP binding is in slow equilibrium with the conformation stabilized in the absence of NADP. FPLC studies have shown that micromolar concentrations of NADP induced oligomerization of G6PD. In addition, the different K0.5 values of NADP binding to the enzyme, ranging from 1-2 microM (from trypsin inactivation) to 90 microM (from titration of the intrinsic fluorescence), suggest a step-wise binding of NADP to the oligomer, with negative cooperativity in the saturation process.

Arginine catabolism in the phototrophic bacterium Rhodobacter capsulatus E1F1. Purification and properties of arginase

The phototrophic bacterium Rhodobacter capsulatus E1F1 grew with L-arginine or L-homoarginine as nitrogen source under light/anaerobiosis. However, when L-arginine was used as the only source of both carbon and nitrogen, the bacterium exhibited weak growth levels and the excess of nitrogen was excreted to the medium as ammonia. By contrast, L-ornithine was used under phototrophic conditions as either nitrogen or carbon source. Other compounds of the arginine catabolic pathways, such as putrescine or proline, also supported phototrophic growth of this bacterium. Under heterotrophic/dark conditions, R. capsulatus always showed a low growth rate with those nitrogen compounds. Cells growing on media containing L-arginine, L-homoarginine or L-ornithine induced an Mn(2+)-dependent arginase activity regardless of the presence of ammonium ions and other readily utilizable nitrogen sources. Arginase activity was strongly inhibited by Zn2+, Cu2+, borate, L-cysteine, L-ornithine and gamma-guanidinobutyrate. Mercurials also inactivated arginase, the activity being partially restored by the presence of thiols. Arginase was purified to electrophoretic homogeneity and found to consist of four identical subunits of 31 kDa. The molecular parameters and kinetic constants of arginase from R. capsulatus E1F1 resembled those previously described for the Saccharomyces cerevisiae enzyme rather than those of bacterial arginases.

An arginine regulated gamma-guanidobutyrate ureahydrolase from tench liver (Tinca tinca L.)

A gamma-guanidobutyrate ureahydrolase isolated from tench liver has been characterized. Some of its physicochemical properties like pH effect and thermal stability resemble those of arginases, however it shows some peculiarities that makes it different from arginases and other amidino hydrolases. Thus cation requirement is not as strong as in arginases, and the Km value for gamma-guanido-butyric acid (230 +/- 25 mM) is shifted to a lower value (45 +/- 5 mM) by 5 mM arginine. The possible regulatory role of arginine on gamma-guanidobutyrate ureahydrolase activity is discussed.

Physico-chemical properties of hepatocyte plasma-membrane-bound arginase

Rat liver plasma-membrane-bound arginase was investigated in order to obtain data regarding its physico-chemical properties. Arginase bound to plasma membrane presented a specific activity of 0.74 +/- 0.09 IU/mg for the fully-activated enzyme, the pH of maximum activity being 9.8. Maximum stability was recorded at two pH values, 7 and 10.5 respectively. Mn2+ activated the enzyme, while Cu2+ and Zn2+, and to a lesser extend Co2+, showed a strong inhibitory effect. Ca2+ and Mg2+ had no effect at the concentrations assayed. The influence of temperature was studied in the presence and in the absence of Mn2+. The enzyme was stable up to 65 degrees C in both cases. Membrane- bound arginase showed an activation energy of 11.5 +/- 1.4 Kcal/mol between 20 and 40 degrees C, and 13.3 +/- 2.5 Kcal/mol between 40 and 60 degrees C. The Q10 for the same temperature ranges were 1.78 and 1.9 respectively. The membrane-bound enzyme presented two different Michaelis constants, one with high affinity (2.05 +/- 0.73 mM) and the other with low affinity for arginine (130 +/- 27.2 mM). Solubilized arginase showed very similar values. Among all the structural analogous assayed, only L-canavanine proved to be substrate for arginase, with and L-arginine/L-canavanine hydrolysis ratio of 5.8 +/- 0.28. No reactivity was found between plasma-membrane-bound arginase and anti-rat liver arginase antibodies raised in rabbits.

Cytopathology of follicular tumours of the thyroid with clear cell change

A retrospective cytological study of nine follicular tumours of the thyroid with clear cell change was undertaken. In five clear cell adenomas and one moderately differentiated clear cell follicular carcinoma the epithelial cells occurred singly or in sheets and clusters; they sometimes assumed a trabecular or follicular pattern. The cells usually had pale diffusely vacuolated cytoplasm with ill-defined boundaries, a variable degree of anisonucleosis, nucleolar enlargement, and nuclear overlapping. Smears from a signet-ring cell adenoma contained in addition a few cells with large cytoplasmic vacuoles and compressed eccentric nuclei. In these cases a cytological diagnosis of 'follicular lesion' (or follicular neoplasia), clear cell type or signet-ring cell type, was given. A cytodiagnosis of 'carcinoma' was made only in the poorly differentiated follicular carcinoma-clear cell variant studied which showed unequivocal features of malignancy. Features suggestive of thyroid cyst, nodular goitre, Hashimoto's thyroiditis, and cell hyperactivity (marginal vacuoles, 'fire flare') were also found in the aspirated specimens of these cases of clear cell tumour of the thyroid.

Properties of arginase immobilized in a fibrin clot

Rat liver arginase was covalently trapped in a fibrin clot. Among the physicochemical properties of the enzyme studied were Mn2+ requirement, pH behavior, temperature and time stability, effect of denaturing agents, and kinetic properties. The immobilized arginase showed the same substrate affinity as soluble arginase, but had higher stability at room temperature, was more resistant to denaturation, and had a higher catalytic activity at physiological pH. The properties so far examined may enhance the use of immobilized arginase in cancer therapy.

Glucose-6-phosphate dehydrogenase from Dicentrarchus labrax liver: kinetic mechanism and kinetics of NADPH inhibition

The kinetic mechanism of the reaction catalyzed by glucose-6-phosphate dehydrogenase (EC 1.1.1.49) from Dicentrarchus labrax liver was examined using initial velocity studies, NADPH and glucosamine 6-phosphate inhibition and alternate coenzyme experiments. The results are consistent with a steady-state ordered sequential mechanism in which NADP+ binds first to the enzyme and NADPH is released last. Replots of NADPH inhibition show an uncommon parabolic pattern for this enzyme that has not been previously described. A kinetic model is proposed in agreement with our kinetic results and with previously published structural studies (Bautista et al. (1988) Biochem. Soc. Trans. 16, 903-904). The kinetic mechanism presented provides a possible explanation for the regulation of the enzyme by the [NADPH]/[NADP+] ratio.

Circadian rhythms in enzymatic activity of rat liver arginase and glucose 6-phosphate dehydrogenase

The circadian rhythms of glucose 6-phosphate dehydrogenase (G6PD) and of arginase activities and total protein content have been studied in the livers of 24-h fasted rats. Both G6PD and arginase activities reach a maximum at night and a minimum during the light period. On the other hand, the total protein level was maximal during the light period while it decreased to its lowest level during the dark period. These results are in agreement with the existence of a lipogenesis-lipolysis circadian rhythm in the rat, since the higher G6PD activity at night provides the necessary NADPH for lipid biosynthesis. The increase in arginase activity is also in agreement with an increase in amino-acid catabolism, probably as a source of energy and metabolic intermediates.