Biotechnological production of <Emphasis Type="SmallCaps">l</Emphasis>-ribose from <Emphasis Type="SmallCaps">l</Emphasis>-arabinose

l-Ribose is a rare and expensive sugar that can be used as a precursor for the production of l-nucleoside analogues, which are used as antiviral drugs. In this work, we describe a novel way of producing l-ribose from the readily available raw material l-arabinose. This was achieved by introducing l-ribose isomerase activity into l-ribulokinase-deficient Escherichia coli UP1110 and Lactobacillus plantarum BPT197 strains. The process for l-ribose production by resting cells was investigated. The initial l-ribose production rates at 39°C and pH 8 were 0.46 ± 0.01 g g⁻¹ h⁻¹ (1.84 ± 0.03 g l⁻¹ h⁻¹) and 0.27 ± 0.01 g g⁻¹ h⁻¹ (1.91 ± 0.1 g l⁻¹ h⁻¹) for E. coli and for L. plantarum, respectively. Conversions were around 20% at their highest in the experiments. Also partially purified protein precipitates having both l-arabinose isomerase and l-ribose isomerase activity were successfully used for converting l-arabinose to l-ribose.     

Effect of pyruvate dehydrogenase complex deficiency on <Emphasis Type="SmallCaps">l</Emphasis>-lysine production with <Emphasis Type="Italic">Corynebacterium glutamicum</Emphasis>

Intracellular precursor supply is a critical factor for amino acid productivity of Corynebacterium glutamicum. To test for the effect of improved pyruvate availability on l-lysine production, we deleted the aceE gene encoding the E1p enzyme of the pyruvate dehydrogenase complex (PDHC) in the l-lysine-producer C. glutamicum DM1729 and characterised the resulting strain DM1729-BB1 for growth and l-lysine production. Compared to the host strain, C. glutamicum DM1729-BB1 showed no PDHC activity, was acetate auxotrophic and, after complete consumption of the available carbon sources glucose and acetate, showed a more than 50% lower substrate-specific biomass yield (0.14 vs 0.33 mol C/mol C), an about fourfold higher biomass-specific l-lysine yield (5.27 vs 1.23 mmol/g cell dry weight) and a more than 40% higher substrate-specific l-lysine yield (0.13 vs 0.09 mol C/mol C). Overexpression of the pyruvate carboxylase or diaminopimelate dehydrogenase genes in C. glutamicum DM1729-BB1 resulted in a further increase in the biomass-specific l-lysine yield by 6 and 56%, respectively. In addition to l-lysine, significant amounts of pyruvate, l-alanine and l-valine were produced by C. glutamicum DM1729-BB1 and its derivatives, suggesting a surplus of precursor availability and a further potential to improve l-lysine production by engineering the l-lysine biosynthetic pathway. This study is dedicated to Prof. Dr. Hermann Sahm on the occasion of his 65th birthday.     

Syntheses of dopa glycosides using glucosidases

Syntheses of l-dopa 1a glucoside 10a,b and dl-dopa 1b glycosides 10–18 with d-glucose 2, d-galactose 3, d-mannose 4, d-fructose 5, d-arabinose 6, lactose 7, d-sorbitol 8 and d-mannitol 9 were carried out using amyloglucosidase from Rhizopus mold, β-glucosidase isolated from sweet almond and immobilized β-glucosidase. Invariably, l-dopa and dl-dopa gave low to good yields of glycosides 10–18 at 12–49% range and only mono glycosylated products were detected through glycosylation/arylation at the third or fourth OH positions of l-dopa 1a and dl-dopa 1b. Amyloglucosidase showed selectivity with d-mannose 4 to give 4-O-C1β and d-sorbitol 8 to give 4-O-C6-O-arylated product. β-Glucosidase exhibited selectivity with d-mannose 4 to give 4-O-C1β and lactose 7 to give 4-O-C1β product. Immobilized β-glucosidase did not show any selectivity. Antioxidant and angiotensin converting enzyme inhibition (ACE) activities of the glycosides were evaluated glycosides, out of which l-3-hydroxy-4-O-(β-d-galactopyranosyl-(1′→4)β-d-glucopyranosyl) phenylalanine 16 at 0.9 ± 0.05 mM and dl-3-hydroxy-4-O-(β-d-glucopyranosyl) phenylalanine 11b,c at 0.98 ± 0.05 mM showed the best IC₅₀ values for antioxidant activity and dl-3-hydroxy-4-O-(6-d-sorbitol)phenylalanine 17 at 0.56 ± 0.03 mM, l-dopa-d-glucoside 10a,b at 1.1 ± 0.06 mM and dl-3-hydroxy-4-O-(d-glucopyranosyl)phenylalanine 11a-d at 1.2 ± 0.06 mM exhibited the best IC₅₀ values for ACE inhibition. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Increased urinary zinc excretion in cancer patients is linked to immune activation and renal tubular cell dysfunction

Urinary zinc excretion is known to be increased in cancer patients, but the pathogenesis of this phenomenon remains uncertain. Both skeletal muscle catabolism and renal tubular cell dysfunction have been proposed to explain this observation. We have investigated urinary zinc and N-acetyl--d-glucosaminidase (NAG), an indicator of renal tubular cell dysfunction, as well as serum neopterin, an index of systemic immune activation, in 22 patients with cancer and seven controls. Both serum neopterin and urinary zinc were significantly elevated in cancer patients (15.8 ± 12.7 versus 7.3 ± 2.3 nmol l^–1 and 1.77 ± 0.80 versus 1.21 ± 0.41 mmol mol^–1 creatinine, P < 0 and P < 0.05, respectively), while NAG was similar in cancer patients and the controls (13.58 ± 13.80 versus 13.68 ± 12.19 kat mol^–1 creatinine). A significant correlation was observed between serum neopterin and urine zinc (rs = 0.5119, P < 0.02), serum neopterin and urine NAG (rs = 0.6761, P < 0.002), and urinary zinc and NAG (rs = 0.6348, P < 0.002). In conclusion, the present data indicate a link between urinary zinc excretion and immune activation as well as renal tubular cell dysfunction. In addition, renal tubular cell dysfunction appears to be linked to immune activation.     

Transport ofl-histidine by human diploid fibroblasts in culture

Summary The transport ofl-histidine has been characterized in skin derived diploid human fibroblasts, cultured under strictly controlled conditions. The transport measurements were made on cells grown to subconfluency after 60 to 90 min timed preincubation. The data, at substrate concentrations ranging from 0.050 to 10 mmol/l, were analyzed by a computer program. A saturable transport system (K _m =0.25 mmol/l, V _max =17 nmol/mg protein per min) and a nonsaturable component of influx (K _d =1.6±0.4 nmol/mg protein/min per mmol) were found.l-Histidine displayed no Na⁺ requirement at either low or high concentrations. Inhibition analysis demonstrated thatl-histidine uptake at low concentration was poorly inhibited by amino acids known to be effective inhibitors of system A. The largest fraction ofl-histidine uptake was inhibited by 2-amino-bicyclo (2,2,1)-heptane-2-carboxylic acid (BCH), leucine, and tryptophan. These results indicated thatl-histidine is transported in human fibroblasts, mainly by the Na⁺ independent system L. The differences between this cell type and others studied previously are discussed. This work was supported in part by Grant 773 from UER de Médecine, Université Paris XI (France).     

Blood plasma concentrations of microelements in endurance trained volunteers during hypokinesia and chronic hyperhydration

The objective of this investigation was to determine the effect of daily intake of fluid and salt supplementation (FSS) on increased urinary losses of microelements that developed during hypokinesia (decreased number of walking steps/d). The studies were performed on 30 endurance-trained male volunteers aged 23–26 yr, with an averaged maximum oxygen uptake of 65 mL/kg/min during 364 d of hypokinesia (HK). All volunteers were divided into three equal groups: Ten volunteers were placed continuously under an average of 10,000 running steps/d (14.2 km/d) (control subjects), ten volunteers subjected continuously to HK without the use of FSS (hypokinetic subjects), and ten volunteers were continuously submitted to HK and consumed daily FSS (hyperhydrated subjects). For the simulation of the hypokinetic effect the hypokinetic and hyperhydrated volunteers were kept under an average of 3,000 walking steps/d (2.7 km/d) for 364 d. Prior to their exposure to HK the volunteers were on an average of 10,000 running steps/d (14.2 km/d). During the prehypokinetic period of 60 d and during the hypokinetic period of 364 d were determined renal excretion of microelements responses of endurance-trained volunteers. In the hyperhydrated volunteers urinary excretion of iron, zinc, copper, manganese, cobalt, nickel, lead, tin, chromium, aluminum, molybdenum, and vanadium decreased, whereas in the hypokinetic volunteers it increased significantly. It was concluded that chronic hyperhydration may be used to attenuate urinary excretion of microelements in endurance-trained volunteers during prolonged restriction of muscular activity.     

Effect of triethylenepentaminehexaacetic acid on the renal damage in cadmium-treated Syrian hamsters

Cadmium (Cd)-induced nephropathy was treated by triethylene-pentaminehexaacetic acid (TTHA) in male Syrian hamsters. Hamsters injected three times a week with 3 mg/kg body wt CdCl₂ showed proteinuria, urinaryN-acetyl-β-d-inglucosaminidase (NAG), and fractional excretion of sodium (FENa) when compared to saline-injected control. Cd-treated hamsters injected ip with TTHA 10 mg/kg body wt five times a week showed reduction of renal damage, including reductions in urinary protein (from 6.7±2.2 to 4.3±0.5 mg/d) and NAG (0.17±0.06 to 0.04±0.02 U/d). Urinary excretion of Cd was significantly increased (from 87±51.3 to 3052±1485 mg/L) by TTHA administration. Cd concentration in renal cortical tissue was slightly reduced (26.4±3.0 to 21.8±2.7 mg/g. protein). Excretion of malondialdehyde (MDA) was increased only in Cd-injected hamsters (to 2.1±1.6 nM/L), and elevated MDA in renal cortical tissue was not reduced by the administration of TTHA (1041±105 vs 1104±358 nM/g protein). Glutathione (GSH) concentration in the renal cortex was significantly elevated after Cd administration and further increased after TTHA administration (5.5±2.1 to 9.8±2.0 μg/50 mg protein). There were no marked effects on creatinine clearance (Ccr) and hematocrit. Moreover, renal morphological changes were improved significantly by treatment with TTHA. We demonstrated the efficacy of TTHA in the treatment of Cd-induced nephropathy in hamsters. Although the precise mechanism of the TTHA effects on Cd-induced nephropathy has not been elucidated, it might involve GSH reducing the elevated MDA concentration in renal tissue.     

Modulation of striatal dopamine release in cerebral ischemia byL-arginine

The effect ofL-arginine, the precursor of nitric oxide, on ischemic dopamine release from the striatum was investigated in Mongolian gerbils subjected to bilateral carotid artery occlusion (15 min) alone or with reflow (2 h). Dopamine and its metabolites were measured in the striatal extracellular space dialysate after continuous perfusion (2 l/min) of artificial extracellular fluid in the presence or absence of 15 mmol/literL- orD-arginine or 1 mmol/liter nitro-L-arginine.L-Arginine but notD-arginine increased the striatal content of dopamine in pre- and postischemia whereas it lowered the levels of dopamine and 3-methoxytyramine induced by ischemia. In contrast, nitro-L-arginine reduced the preischemic levels of dopamine and 3,4-dihydroxyphenyl-acetic acid, and had no effect on the ischemic release of dopamine. These findings indicate thatL-arginine stereospecifically modified the ischemic release and metabolism of dopamine. The data also suggest that the basal level of nitric oxide is not involved in dopamine release during ischemia but may participate in regulating dopamine release under physiological conditions.Presented in part at the 19th International Joint Conference on Stroke and Cerebral Circulation, San Diego, California, February 17–19, 1994.     

Acetyl-l-carnitine influences the fluidity of brain microsomes and of liposomes made of rat brain microsomal lipid extracts

The fluorescence anisotropy (r) of diphenylhexatriene (DPH) was measured in different preparations (bovine spinal cord phosphatidylserine liposomes, rat brain microsomes, liposomes made with rat brain microsomal lipid having different phospholipid:cholesterol ratios) at temperatures ranging from 10° to 55°C. Phosphatidylserine liposomes exhibited an exponential relationship of rversus temperature, whereas the relationship shown by microsomes and liposomes prepared with microsomal lipid extracts was a linear one. The removal of protein and high phospholipid:cholesterol ratios decreased the slope of the lines (fluidity increased), although the intercept was unaffected. This means that differences were better appreciated at high temperatures and were well evident at 37°C. Acetyl-l-carnitine decreased r in rat brain microsomes and in liposomes made with microsomal lipids with different phospholipid:cholesterol ratios. The fluidifying effect of acetyl-l-carnitine was mild but statistically significant and could explain, at least in part, the data reported in the literature of acetyl-l-carnitine acting on some parameters affected by ageing. Besides, acetyl-l-carnitine seemed to oppose the changes of viscosity due to lipid peroxidation, which has been reported to increase in ageing and dementia.l-carnitine shares the properties of its acetyl ester, but only in part.Abbreviations DPH diphenylhexatriene - HEPES 4-(2-hydroxyethyl-l-piperazineethansulfonic) acid - r fluorescence anisotropy - SHB sucrose-HEPES-buffer (0.32 M sucrose, 2 mM HEPES, pH 7.0)     

d-Aminoaciduria in mutant mice lackingd-amino-acid oxidase activity

Summary Urine of mutant ddY/DAO^– mice lackingd-amino-acid oxidase activity contained more serine and proline than that of normal ddY/DAO⁺ mice.d-Amino-acid oxidase treatment of urinary amino acids decreased the serine and proline, suggesting that they containedd-isomers. An HPLC analysis confirmed the presence ofd-serine. Urinary serine and proline contents were not decreased when the ddY/DAO^– mice were fed a diet which did not contain supplementaryd-methionine or when they were given water containing antibiotics. These results suggest that thed-serine andd-proline do not derive from thed-methionine supplemented in the diet or from intestinal bacteria. In urine of the ddY/DAO^– mice, a substance which seemed to bed-methionine sulfoxide and/ord-methionine sulfone was present. It is probably a metabolite of thed-methionine supplemented in the diet. Thed-aminoaciduria in the mutant mice lackingd-amino-acid oxidase activity indicates that this enzyme is involved in the metabolism of thed-amino acids in normal mice.     

Purification and characterization of <Emphasis Type="SmallCaps">l</Emphasis>-arabinose isomerase from <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> producing <Emphasis Type="SmallCaps">d</Emphasis>-tagatose

l-arabinose isomerase (EC5.3.1.4. AI) mediates the isomerization of d-galactose into d-tagatose as well as the conversion of l-arabinose into l-ribulose. The AI from Lactobacillus plantarum SK-2 was purified to an apparent homogeneity giving a single band on SDS–PAGE with a molecular mass of 59.6 kDa. Optimum activity was observed at 50°C and pH 7.0. The enzyme was stable at 50°C for 2 h and held between pH 4.5 and 8.5 for 1 h. AI activity was stimulated by Mn²⁺, Fe³⁺, Fe²⁺, Ca²⁺ and inhibited by Cu²⁺, Ag⁺, Hg²⁺, Pb²⁺. d-galactose and l-arabinose as substrates were isomerized with high activity. l-arabitol was the strongest competitive inhibitor of AI. The apparent Michaelis–Menten constant (K _m), for galactose, was 119 mM. The first ten N-terminal amino acids of the enzyme were determined as MLSVPDYEFW, which is identical to L. plantarum (Q88S84). Using the purified AI, 390 mg tagatose could be converted from 1,000 mg galactose in 96 h, and this production corresponds to a 39% equilibrium.     

A Metal Ion as a Cofactor Attenuates Substrate Inhibition in the Enzymatic Production of a High Concentration of <Emphasis Type="SmallCaps">D</Emphasis>-glutamate Using <Emphasis Type="Italic">N</Emphasis>-acyl-<Emphasis Type="SmallCaps">D</Emphasis>-glutamate Amidohydrolase

N-Acyl-D-glutamate amidohydrolase (D-AGase) was inhibited by 94 % when 1 mol/l N-acetyl-DL- glutamate was used as a substrate. The addition of 1 mM Co²⁺ stabilized D-AGase. Moreover, the substrate inhibition was weakened to 88% with the addition of 0.4 mM Co²⁺ to the reaction mixture. Although D-AGase is a zinc-metalloenzyme, the addition of Zn²⁺ from 0.01 to 10 mM did not increase the D-glutamic acid production in the saturated substrate. Under optimal conditions, 0.38 M D-glutamic acid was obtained from N-acyl-DL-glutamate with 100% of the theoretical yield after 48 h.     

Isolation of <Emphasis Type="Italic">Aspergillus oryzae</Emphasis> mutants for heterologous protein production from a double proteinase gene disruptant

The recombinant Pichia pastoris harboring an improved methionine adenosyltransferase (MAT) shuffled gene was employed to biosynthesize S-adenosyl-l-methionine (SAM). Two l-methionine (l-Met) addition strategies were used to supply the precursor: the batch addition strategy (l-Met was added separately at three time points) and the continuous feeding strategies (l-Met was fed continuously at the rate of 0.1, 0.2, and 0.5 g l⁻¹ h⁻¹, respectively). SAM accumulation, l-Met conversion rate, and SAM productivity with the continuous feeding strategies were all improved over the batch addition strategy, which reached 8.46 ± 0.31 g l⁻¹, 41.7 ± 1.4%, and 0.18 ± 0.01 g l⁻¹ h⁻¹ with the best continuous feeding strategy (0.2 g l⁻¹ h⁻¹), respectively. The bottleneck for SAM production with the low l-Met feeding rate (0.1 g L⁻¹ h⁻¹) was the insufficient l-Met supply. The analysis of the key enzyme activities indicated that the tricarboxylic acid cycle and glycolytic pathway were reduced with the increasing l-Met feeding rate, which decreased the adenosine triphosphate (ATP) synthesis. The MAT activity also decreased as the l-Met feeding rate rose. The reduced ATP synthesis and MAT activity were probably the reason for the low SAM accumulation when the l-Met feeding rate reached 0.5 g l⁻¹ h⁻¹.     

Effect of acetyl-l-carnitine on lipid peroxidation and xanthine oxidase activity in rat skeletal muscle

It has been reported that acetyl-l-carnitine (AcCn) can reduce the degenerative processes in the central nervous system of rats, modify the fluidity of membranes and decrease the accumulation of lipofuscins in neurones. In light of these considerations we have assayed the in vitro effect of acetyl-l-carnitine on spontaneous and induced lipoperoxidation in rat skeletal muscle; in addition, the effect of AcCn on XD/XO ratio was evaluated. The presence of AcCn (10–40 mM) in incubation medium significantly reduced MDA and conjugated diene formation in rat skeletal muscle; moreover, a significant decrease in induced MDA levels was observed when microsomal preparation where incubated in the presence of 10–40 mM AcCn. Since a significant reduction of XO activity was detected in the presence of 10–80 mM AcCn, the reduced lipid peroxidation by AcCn seems to be due to an inhibition of XO activity.     

Intracellular Delivery of Nanoparticles of an Antiasthmatic Drug

The aim of the investigation was to prepare and characterize wheat germ agglutinin(WGA)-conjugated poly(d,l-lactic-co-glycolic) acid nanoparticles encapsulating mometasone furoate (MF) as a model drug and assess changes in its fate in terms of cellular interactions. MF loaded nanoparticles were prepared using emulsion–solvent evaporation technique. WGA-conjugation was done by carbodiimide coupling method. The nanoparticles were characterized for size, zeta potential, entrapment efficiency and in-vitro drug release. The intracellular uptake of nanoparticles, drug cellular levels, and anti-proliferative activity studies of wheat germ agglutinin-conjugated and unconjugated nanoparticles were assessed on alveolar epithelial (A549) cells to establish cellular interactions. Prepared nanoparticles were spherical with 10–15 μg/mg of WGA conjugated on nanoparticles. The size of nanoparticles increased after conjugation and drug entrapment and zeta potential reduced from 78 ± 5.5% to 60 ± 2.5% and −15.3 ± 1.9 to −2.59 ± 2.1 mV respectively after conjugation. From the cellular drug concentration–time plot, AUC was found to be 0.4745, 0.6791 and 1.24 for MF, MF-nanoparticles and wheat germ agglutinin-MF-nanoparticles respectively. The in-vitro antiproliferative activity was improved and prolonged significantly after wheat germ agglutinin-conjugation. The results conclusively demonstrate improved availability and efficacy of antiasthmatic drug in alveolar epithelial cell lines. Hence, a drug once formulated as mucoadhesive nanoparticles and incorporated in dry powder inhaler formulation may be used for targeting any segment of lungs for more improved therapeutic response in other lung disorders as well.     

Overproduction of glutathione by <Emphasis Type="SmallCaps">l</Emphasis>-cysteine addition and a temperature-shift strategy

The present study investigated the effects of three constituent amino acids on glutathione production in flask culture of Candida utilis. Although l-glutamic acid and glycine had little impact on cell growth and glutathione biosynthesis, l-cysteine positively influenced glutathione production, despite inhibiting cell growth when it was added prior to stationary phase. Adding 8 mmol/L of l-cysteine to the culture broth at 16 h boosted glutathione production by 91%, increasing the intracellular glutathione content by 106% compared to untreated controls. A temperature-shift strategy, in which we shifted batch and fed-batch cultures of C. utilis from 30 to 26°C, also significantly enhanced glutathione production. Applying both strategies (i.e. adding 20 mmol/L l-cysteine and shifting the temperature from 30 to 26°C) at 33 h enhanced the glutathione concentration and the intracellular glutathione content to 1,312 mg/L and 3.75%, respectively, during fed-batch cultivation (glucose feeding at a constant rate of 18.3 g/h). The average specific glutathione production rate under this condition was 129% higher than that of the control without strategy.     

Effect of aluminum on the blood-brain barrier permeability during nitric oxide-blockade-induced chronic hypertension in rats

We examined the effect of aluminum on the permeability of the blood-brain barrier (BBB) during nitric oxide-blockade-induced chronic hypertension in rats. Animals were given the inhibitor of nitric oxide synthase, l-NAME (N ^ω-nitro-l-arginine methyl ester), for 4 wk to induce chronic hypertension. Two groups of rats were given an intraperitoneal injection of aluminum chloride. The integrity of the BBB was assessed by a quantitative measurement for Evans blue (EB) dye. The arterial blood pressure in l-NAME- and l-NAME plus aluminum-treated animals was significantly elevated from 115±2.8 and 110±1.7 mm Hg to 174±5.2 and 175±4.8 mm Hg, respectively (p<0.01). The EB dye content in the brain regions of the rats in the l-NAME group was increased, but there was no statistical significance compared to the saline group. The extravasation of EB dye was significantly increased in the brain regions of the animals treated with aluminum compared to the rats treated with saline (p<0.05). A significantly higher EB dye content in the brain regions was observed in the l-NAME plus aluminium group compared to l-NAME, aluminum, and saline groups (p<0.01). These findings indicate that exposure to a high level of aluminum leads to an additional increase in BBB permeability where nitric oxide-blockade-induced chronic hypertension potentiates the effect of aluminum to enhance BBB permeability to EB dye.     

Characterization of <Emphasis Type="SmallCaps">d</Emphasis>-tagatose-3-epimerase from <Emphasis Type="Italic">Rhodobacter sphaeroides</Emphasis> that converts <Emphasis Type="SmallCaps">d</Emphasis>-fructose into <Emphasis Type="SmallCaps">d-</Emphasis>psicose

A non-characterized gene, previously proposed as the d-tagatose-3-epimerase gene from Rhodobacter sphaeroides, was cloned and expressed in Escherichia coli. Its molecular mass was estimated to be 64 kDa with two identical subunits. The enzyme specificity was highest with d-fructose and decreased for other substrates in the order: d-tagatose, d-psicose, d-ribulose, d-xylulose and d-sorbose. Its activity was maximal at pH 9 and 40°C while being enhanced by Mn²⁺. At pH 9 and 40°C, 118 g d-psicose l⁻¹ was produced from 700 g d-fructose l⁻¹ after 3 h. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Purification and characterization of anl-amino-acid oxidase fromChlamydomonas reinhardtii

Anl-amino-acid oxidase (EC 1.4.3.1) that catalyzes the oxidative deamination of twelvel-amino acids has been purified 21-fold and with 14% yield to electrophoretic homogeneity fromChlamydomonas reinhardtii cells by ammonium-sulfate fractionation, gel filtration through Sephacryl and Superose, anion-exchange chromatography and preparative electrophoresis in polyacrylamide gels. The native enzyme is a protein of 470 kDa and consists of eight identical or similarsized subunits of 60 kDa each. Optimum pH and temperature were 8.2 and 55° C, respectively, with a Q₁₀ (45–55° C) of 1.7 and an activation energy of 45 kJ · mol^–1. Its absorption spectrum showed, in the visible region, maxima at 360 and 444 nm, characteristic of a flavoprotein with a calculated flavin content of 7.7 mol FAD per mol of native enzyme. ApparentK _m values of the twelvel-amino acids which can act as substrates ofl-amino-acid oxidase ranged between 31 M for phenylalanine and 176 M for methionine. The effect of several specific group reagents, chelating agents and bivalent cations on enzyme activity has also been studied.This work was supported by Grant 780-CO2-01 from CICYT, Spain. The skillful secretarial assistance of C. Santos and I. Molina is gratefully acknowledged.     

Prolonged inhibition of brain nitric oxide synthase by short-term systemic administration of nitro-l-arginine methyl ester

We studied the dose-response characteristics and the temporal profile of inhibition of brain nitric oxide (NO) synthase (NOS) elicited by i.v. administration of the NOS inhibitor nitro-l-arginine methyl ester (L-NAME). L-NAME was administered i.v. in awake rats equipped with a venous cannula. L-NAME was injected in cumulative doses of 5, 10, 20 and 40 mg/kg and rats were sacrificed 30 min after the last dose. NOS catalytic activity was assayed in forebrain cytosol as the conversion of [³H]l-arginine into [³H]l-citrulline. L-NAME attenuated brain NOS activity in a dose-dependent manner but enzyme activity could not be inhibited by more than 50%. After a single 20 mg/kg injection of L-NAME the inhibition of brain NOS activity was time dependent and reached a stable level at 2 hrs (52% of vehicle). Inhibition after a single injection was still present at 96 hrs, albeit to a lower magnitude. We conclude that intravenous administration of L-NAME in rats at concentrations commonly used in physiological experiments leads to a dose and time-dependent but partial inhibition of brain NOS catalytic activity. The finding that the inhibition persists for several days after a single administration is consistent with the hypothesis that nitro-L-arginine, the active principle of L-NAME, binds to NOS irreversibly.