Effects of delta-aminolaevulinic acid on contractile activity in the isolated small intestine of the rabbit. Role of adrenergic receptors

The porphyrin precursor, delta-aminolaevulinic acid (ALA) at concentrations of 0.23-7.6 mM caused dose-dependent inhibition of spontaneous contractions in isolated preparations of rabbit small intestine, suspended in Ringer-Locke solution. Contractions which returned after inhibition from 3.8 and 7.6mM ALA showed increased amplitude and from 7.6 mM ALA a reduction in rate. Pretreatment with prazosin (10(-7) M) significantly reduced the duration of inhibition exerted by 3.8 and 7.6 mM ALA and also the amplitude of contractions returning after this inhibition. Pretreatment with yohimbine (10(-6) M) and propranolol (7 X 10(-6) M) had no significant effects. Blocking of the release of noradrenaline in preparations by incubation with 6-hydroxydopamine (10(-3) M) or guanethidine (1.5 X 10(-5) M) did not prevent the inhibitory effects of ALA. The alpha 1 agonist, cirazoline (10(-5) M), inhibited contractile activity. This effect was blocked by prazosin (10(-7) M). The alpha 2 agonist, guanoxabenz (10(-5) M) had no detectable effect, in the presence of prazosin, to block any residual alpha 1 actions. It is concluded that alpha 1 receptors mediate inhibitory effects in this preparation and that ALA appears to have direct effects upon these receptors.

Neuropharmacology of delta-aminolaevulinic acid. II. Effect of chronic administration in mice

delta-Aminolaevulinic acid (ALA) is suspected of being responsible for the neuropsychiatric symptoms of acute porphyria. The object of this study was to examine the effects of continuous administration of ALA in vivo on behaviour known to be affected in acute porphyria. ALA was administered to mice via minipumps implanted subcutaneously. Mean urinary excretion of ALA over the ensuing 7 days was approximately 80 mumol/kg b. wt./day. No significant effects on locomotor activity, motor co-ordination and grip and noci-perception were noted. These results do not support the hypothesis that chronic exposure of animals to ALA may produce a porphyria-like syndrome.

Regulation of delta-aminolaevulinic acid synthesis and protochlorophyllide regeneration in the leaves of dark-grown barley (Hordeum vulgare) seedlings

Laevulinic acid (Lev) was used to control the rate of protocholorophyllide (PChl) regeneration in the leaves of dark-grown seedlings of barley (Hordeum vulgare) after a brief light treatment. In the leaves given Lev, at concentrations that severely block the resynthesis of protochlorophyllide, there was a massive overproduction of delta-aminolaevulinic acid (AmLev) that was well in excess of that required for the regeneration of PChl observed in the control leaves. Lev, at low concentrations, slightly delayed regeneration and held up, rather than inhibited, the utilization of the AmLev, which accumulated in the tissues. The overproduction and uncontrolled formation of AmLev also occurred in dark-grown leaves treated with a high concentration of Lev and given a light treatment of just sufficient energy to photoreduce only small quantities of the endogenous PChl. Experiments in which a high level of free PChl was induced by incubating the leaves in AmLev indicated that the active species of PChl was that associated with, and bound to, the PChl reductase protein. The results strongly demonstrate a close relationship between the PChl-protein complex and the ability of the leaves to synthesize AmLev.

Neuropharmacology of delta-aminolaevulinic acid--I. Effect of acute administration in rodents

Delta-aminolaevulinic acid (ALA) is suspected of being responsible for the neuropsychiatric symptoms of acute porphyria. The object of this study was to examine the effects of ALA in vivo on a range of behavioural and physiological functions which are known to be affected in the acute porphyric attack. Aminolaevulinic acid was administered by intraperitoneal or subcutaneous injection to mice in doses up to 1000 mg/kg and effects on nociception (hot-plate and abdominal constriction tests), CNS excitability (pentobarbitone sleep-time and pentylenetetrazole-induced seizures), motor co-ordination and grip (rotating rod test) were studied. Rats were given intravenous injections or infusions of ALA of up to 24 mg and changes in blood pressure, heart rate and ED50 for noradrenaline, acetylcholine and isoprenaline examined. No statistically significant effects were noted, using buffered solutions of ALA (pH 7.0-7.4). However, unbuffered solutions of ALA caused significant bradycardia and hypotension. These results do not support the hypothesis that ALA has significant acute neuropharmacological activity in vivo when the blood-brain barrier is intact.

The effect of delta-aminolaevulinic acid on the high affinity uptake of aspartic acid by rat brain synaptosomes

delta-Aminolaevulinic (delta-ALA) acid is an analogue of GABA, glutamate and aspartate. High affinity GABA uptake by synaptosomes is inhibited by delta-ALA in a competitive fashion at high concentrations (greater than 0.5 mM). Glutamate uptake is inhibited in a non-competitive fashion at all delta-ALA concentrations (0.05-2.0 mM). High affinity aspartate uptake is inhibited in a non-competitive fashion at high concentration (greater than 1.0 mM) but exhibits a curve which resembles that for the inhibition of GABA uptake. The different interactions between delta-ALA, glutamate and aspartate may be evidence for a separate transport system for aspartate.

Inhibition of Na+, K+-ATPase activity by delta-aminolevulinic acid

delta-Aminolaevulinic acid (ALA) has been shown to be toxic to cultured neurons and glia at concentrations as low as 10 microM. In an attempt to elucidate the mechanism of toxicity, the effects of ALA on membrane ATPase activity were investigated. Exposure of neuron cultures to 1 mM ALA for 7 days caused a substantial decrease in both Na+, K+-ATPase and Mg2+-ATPase activities. At lower concentrations, ALA affected only the Na+, K+-component. ALA appeared to act directly, inhibiting Na+, K+-ATPase activity in rat brain cortex membrane preparations at 10 microM. Although this effect was slight, it may well represent the mechanism of action of ALA, since ouabain, a potent inhibitor of Na+, K+-ATPase activity, proved to be more toxic to cultured neurons than ALA. Furthermore, cardiac glycoside overdosage causes neurological disturbances which are very similar to those observed in the acute attack of porphyria.

Hemodynamic effects of high dosages of verapamil and the lack of protection by 4-aminopyridine in the rabbit

4-Aminopyridine (1 mg/kg) restored a 35% fall in arterial blood pressure in rabbits evoked by a verapamil infusion (0.5 mg/kg/min) more effectively than calcium-levulate (approx. 13 mg/kg). However, the lethal dose of verapamil for rabbits (mean: 7.1 mg/kg given by intravenous infusion in 14.3 min) was not affected by 4-aminopyridine pretreatment.

Molecular-organization and biosynthesis of pigment-protein complexes of Rhodopseudomonas capsulata

The photosynthetic apparatus of the facultative phototrophic bacterium Rhodopseudomonas capsulata contains three bacteriochlorophyll-carotenoid-protein complexes: the reaction center and the light-harvesting (LH) antenna complexes LHI (B870) and LHII (B800--850). In contrast to green anoxygenic phototrophic bacteria and the oxygenic cyanobacteria, the light-harvesting complexes of Rhodospirillaceae and Chromatiaceae are integral membrane particles. Variations in light fluxes induce membrane differentiation mainly expressed as variations in the size of the photosynthetic unit and in the area of intracytoplasmic membrane per cell. The B800--850 complex is the variable part of the photosynthetic apparatus. Synthesis of bacteriochlorophyll and of the polypeptides of the pigment complexes was found to be strongly coordinated. The synthesis of these polypeptides was followed immediately by the assembly of the complexes in the membrane. Bacteriochlorophyll or a signal substance triggered by bacteriochlorophyll synthesis regulated the synthesis of these polypeptides at the level of translation. The pigment-binding subunits of the B800--850 complex form oligomeric structures which interact with subunit H of the reaction center. A model of the topographical relationships of the pigment complexes is discussed.

Failure of delta-aminolaevulinic acid and porphobilinogen to alter renal salt and water excretion in the dog

We tested the hypothesis that the hyponatremia commonly observed in patients with acute hepatic porphyria is mediated by the presence of aminolaevulinic acid (ALA) and (or) porphobilinogen (PBG) at the level of the renal tubule to alter water handling, or at the level of the nervous system to release antidiuretic hormone (ADH). When these substances were infused intravenously into hydropenic dogs, there was no effect on systemic hemodynamics or renal function. Neither ALA or PBG, when infused directly into the renal circulation of water-loaded dogs, could effect a decrease in urinary flow, osmolar clearance, or renal perfusion. Similar results were obtained when these substances were infused directly into the renal circulation of hydropenic dogs. When ALA was administered directly into the carotid artery of nine water-loaded dogs and eight hydropenic dogs, there was again no effect on systemic hemodynamics or renal function. These data suggest that ALA (and PBG) have no effect on the renal excretion of sodium or water, and ALA does not cause the release of ADH. The hyponatremia of porphyria may be related to factors other than the elevated plasma levels of ALA and PBG.

The effects of succinylacetone (4,6-dioxoheptanoic acid) on delta-aminolevulinate synthase activity and the content of heme in monolayers of chick embryo liver cells

Succinylacetone was shown to inhibit aminolevulinate dehydratase (5-aminolevulinate hydro-lyase (adding 5-aminolevulinate and cyclizing), EC 4.2.1.24) to reduce cellular heme and porphyrins and to induce delta-aminolevulinate synthase (succinyl-CoA:glycine C-succinyltransferase (decarboxylating), EC 2.3.1.37) in monolayers of chick embryo liver cells. Marked synergistic effects on delta-aminolevulinate synthase activity were obtained by combining succinylacetone with levulinate and porphyrogenic drugs. The time course of delta-aminolevulinate synthase activity showed a delayed synergistic response.

Inhibition by glutamate of phosphate-dependent glutaminase of rat kidney

A membrane-associated form of phosphate-dependent glutaminase was derived from sonicated mitochondria and purified essentially free of gamma-glutamyl transpeptidase activity. Increasing concentrations of phosphate cause a sigmoidal activation of the membrane-bound glutaminase. Phosphate also causes a similar effect on the rate of glutaminase inactivation by the two affinity labels, L-2-amino-4-oxo-5-chloropentanoic acid and 6-diazo-5-oxo-L-norleucine, as observed previously for the solubilized and purified enzyme. Therefore the two forms of glutaminase undergo similar phosphate-induced changes in conformation. A sensitive radioactive assay was developed and used to determine the kinetics of glutamate inhibition of the membrane-associated glutaminase. The Km for glutamine decreases from 36 to 4 mM when the phosphate concentration is increased from 5 to 100 mM. Glutamate is a competitive inhibitor with respect to glutamine at both high and low concentrations of phosphate. However, the Ki for glutamate is increased from 5 to 52 mM with increasing phosphate concentration. Therefore glutamine and glutamate interact with the same site on the glutaminase, but the specificity of the site is determined by the available phosphate concentration.

Effects of delta-aminolaevulinic acid, porphobilinogen and structurally related amino acids on 2-deoxy-glucose uptake in cultured neurons

The effects of delta-aminolaevulinic acid (ALA), porphobilinogen (PBG), gamma amino-butyric acid (GABA), muscimol, glutamic acid and kainic acid on [3H]2-deoxy-D-glucose uptake by cultured neurons were investigated. Exposure to the cultures for 4 days, to ALA at concentrations as low as 10 microM caused a significant, dose-dependent decrease in [3H] 2-deoxy-D-glucose uptake. Neither ALA nor PBG appeared to interfere directly with glucose transport into the neuron but 1 mM ALA caused an initial stimulation of [3H] 2-deoxy-D-glucose uptake which increased to a maximum after 4 hr and fell to below control values after 19 hr exposure. GABA and muscimol caused similar increases in [3H] 2-deoxy-D-glucose uptake but these values remained above control levels after 19 hr exposure. Glutamic acid and kainic acid caused an immediate increase in [3H] 2-deoxy-D-glucose uptake which declined to minimum values after 4 hr exposure. The effect of ALA on glucose utilization in neurons may be of particular relevance to patients with acute porphyria where a genetic lesion in neural haem and haemoprotein biosynthesis is postulated to occur. ALA appeared to be more toxic to the neurons than any of the other compounds tested, possibly causing a critical depletion of energy reserves and cell death.

Effects of iron deficiency on heme biosynthesis in Rhizobium japonicum

The effects of iron deficiency on heme biosynthesis in Rhizobium japonicum were examined. Iron-deficient cells had a decreased maximum cell yield and a decreased cytochrome content and excreted protoporphyrin into the growth medium. The activities of the first two enzymes of heme biosynthesis, delta-aminolevulinic acid synthase (EC 2.3.1.37) and delta-aminolevulinic acid dehydrase (EC 4.2.1.24), were diminished in iron-deficient cells, but were returned to normal levels upon addition of iron to the cultures. The addition of iron salts, iron chelators, hemin, or protoporphyrin to cell-free extracts did not affect the activity of these enzymes. The addition of levulinic acid to iron-deficient cultures blocked protoporphyrin excretion and also resulted in high delta-aminolevulinic acid synthase and delta-aminolevulinic acid dehydrase activities. These results suggest the possibility that rhizobial heme biosynthesis in the legume root nodule may be affected by the release of iron from the host plant to the bacteroids.

Delta-Aminolaevulinic acid and amino acid neurotransmitters

The effects of the porphyrin precursor delta-aminolaevulinic acid (ALA) on gamma-aminobutyric acid (GABA) and L-glutamate transmitter systems was investigated in rat brain. It was found that ALA inhibited GABA and glutamate uptake and stimulated basal efflux of the amino acids in purified nerve endings. These effects were evident only at relatively high concentrations of ALA (at least 100 microM). Such concentrations probably do not occur in the nervous systems of patients suffering from acute porphyria. In addition, it was found that ALA inhibited the stimulated release of GABA from nerve endings probably by acting as an agonist at GABA autoreceptors. This effect was found at very low concentrations of ALA (1 microM). It is therefore likely that the neuropsychiatric manifestations of the acute porphyric attack are attributable, to some extent, to reduced GABA release at central synapses.

[Mechanism of delta-aminolevulinic acid neurotoxicity]

The neurotoxicity of delta-aminolaevulinic acid (ALA), porphobilinogen (PBG), glutamic acid, gamma-aminobutyric acid and kainic acid was compared in order to investigate the possibility of a common neurotoxic mechanism. Only ALA (10 microM) and glutamic acid (1 mM) were toxic towards neurons in culture, as measured by cell survival after 5 days' exposure. 3H-kainic acid binds to striatal membranes with an equilibrium dissociation constant (KD) of 57 nM and the number of binding sites was found to be 20 pmol/g striatal tissue. However, neither of the porphyrin precursors could displace kainic acid from these binding sites. Kainic acid alone caused neuronal degeneration after intrastriatal administration, as determined by 3H-spiroperidol binding to striatal membranes. The porphyrin precursors ALA and PBG thus do not share a common neurotoxic mechanism with the well-known neurotoxin kainic acid.

delta-Aminolaevulinic acid uptake, toxicity, and effect on [14C]gamma-aminobutyric acid uptake into neurons and glia in culture

delta-Aminolaevulinic acid (ALA) uptake into neurons and glia in primary culture as well as ALA toxicity and its effects on gamma-aminobutyric acid (GABA) uptake were examined. [4-14C]ALA uptake into neurons and glia was nonsaturable, partially Na+- and temperature-dependent, and appeared to comprise mainly diffusion into the cell. 2,4-Dinitrophenol caused some inhibition of [4-14C]ALA uptake whereas ouabain, KCN, or amino acids at 1 mM concentration were without effect. ALA (1 mM) caused a slight inhibition of [U-14C]GABA uptake into neurons (14%) and glia (9%), but was without effect at lower concentrations. It is unlikely that, in acute porphyria, ALA reaches sufficiently high levels in nervous tissue to interfere with the reuptake of GABA into neurons or glia. ALA was shown to be toxic, judged by the loss of cells, to both neurons and glia at concentrations as low as 10 microM. Such a concentration of ALA may be expected to occur in the CSF of porphyric patients in the acute attack. However, results obtained with dispersed cells in culture may not necessarily reflect the situation in vivo where the cell may have a far greater resistance to the effects of toxic agents.

5-Aminolevulinic acid dehydratase: alkylation of an essential thiol in the bovine-liver enzyme by active-site-directed reagents

1. 5-Aminolevulinic acid dehydratase from bovine liver has been shown to be inactivated by 5-halolevulinic acids and 3-halolevulinic acids. 2. The substrate, 5-aminolevulinic acid, protects the enzyme from modification by 5-halolevulinic acids. 3. Using tritiated chlorolevulinic acids, it was shown that four of the subunits in the octameric enzyme are preferentially modified. 4. The susceptible enzyme group modified is an --SH group of a reactive cysteine at or near the active site. 5. Oxidized enzyme is not affected by either 5-chlorolevulinic acid or 3-chlorolevulinic acid. 6. Evidence is presented which suggests that 5-chlorolevulinic acid is acting as an active-site-directed reagent.

Purification, properties and synthesis of delta-aminolaevulinate dehydratase from Neurospora crassa

Delta-aminolaevulinate dehydratase, the second and rate-limiting enzyme of the haem-biosynthetic pathway, was purified 300-fold from induced cultures of Neurospora crassa. The native enzyme has a mol.wt. of about 350000, whereas the salt-treated enzyme after incubation at 37 degrees C for 10 min has a mol.wt. of about 232000. The mol.wt. of the subunit is about 38000. Antibodies to the purified enzyme were raised in rabbits. By using radiolabelling and immunoprecipitation techniques it was shown that addition of iron and laevulinate to iron-deficient cultures brings about a significant increase in the synthesis of the enzyme, and protoporphyrin, the penultimate end product of the pathway, represses enzyme synthesis.

The effect of delta-aminolevulinate on catalase T-messenger RNA levels in delta-aminolevulinate synthase-defective mutants of Saccharomyces cerevisiae

Total RNA was isolated from mutants of Saccharomyces cerevisiae that lack active delta-aminolevulinate synthase and are therefore defective in heme biosynthesis. The RNAs were translated in the cell-free protein synthesis system from wheat germ, and the catalase T synthesized was isolated by immunoadsorption and polyacrylamide gel electrophoresis in the presence of dodecyl sulfate. Little or no catalase T product was detected with RNA from mutant cells grown in the absence of a heme precursor. As judged from in vitro translational capacity, RNA fractions from mutant cells grown in the presence of delta-aminolevulinate contained at least 10 times more catalase T mRNA than RNA from unsupplemented cells.

Effects of delta-aminolaevulinic acid on contractile activity of rabbit duodenum

delta-Aminolaevulinic acid (ALA) inhibited spontaneous contractions and contractions induced by acetylcholine, barium chloride or ouabain in rabbit duodenum preparations suspended in Ringe-Locke solution. Concentrations of ALA between 25--100 micrograms/ml reduced amplitude of spontaneous contractions and at levels above 200 micrograms ALA/ml spontaneous contractions caused. Muscle tone was decreased in proportion to logarithm of AL concentration between 25 and 1000 micrograms/ml. Gut ALA levels were increased by the treatment and returned to control values after washing, and pharmacological effects were full reversed. Neither tetrodotoxin nor atropine affected the gut's response to ALA. The response still occurred in calcium-free, high-calcium, potassium-free and high-potassium bathing fluid. Effects of ouabain resembled those of ALA only when gut had been pretreated with atropine; pretreatment with tetrodotoxin induced slight contracture. The observed pharmacological effects of ALA must be by actions additional to sodium pump inhibition.

The effect of delta-aminolevulinic acid on the synthesis and metabolism of GABA in rabbit brain homogenates

The porphyrin precursor delta-aminolevulinic acid (delta-ALA) is a structural analogue of the putative amino acid neurotransmitter, gamma-aminobutyric acid (GABA). This study has demonstrated that delta-ALA has no effect on glutamate decarboxylase activity and only a small inhibitory effect of GABA aminotransferase activity. This would suggest that if accumulation of delta-ALA is related to development of the acute attack of porphyria, it is not via an effect on GABA synthesis and metabolism.