Diet-induced muscle insulin resistance in rats is ameliorated by acute dietary lipid withdrawal or a single bout of exercise: parallel relationship between insulin stimulation of glucose uptake and suppression of long-chain fatty acyl-CoA

Chronic high-fat feeding in rats induces profound whole-body insulin resistance, mainly due to effects in oxidative skeletal muscle. The mechanisms of this reaction remain unclear, but local lipid availability has been implicated. The aim of this study was to examine the influence of three short-term physiological manipulations intended to lower muscle lipid availability on insulin sensitivity in high-fat-fed rats. Adult male Wistar rats fed a high-fat diet for 3 weeks were divided into four groups the day before the study: one group was fed the normal daily high-fat meal (FM); another group was fed an isocaloric low-fat high-glucose meal (GM); a third group was fasted overnight (NM); and a fourth group underwent a single bout of exercise (2-h swim), then were fed the normal high-fat meal (EX). In vivo insulin action was assessed using the hyperinsulinemic glucose clamp (plasma insulin 745 pmol/l, glucose 7.2 mmol/l). Prior exercise, a single low-fat meal, or fasting all significantly increased insulin-stimulated glucose utilization, estimated at either the whole-body level (P < 0.01 vs. FM) or in red quadriceps muscle (EX 18.2, GM 28.1, and NM 19.3 vs. FM 12.6 +/- 1.1 micromol x 100 g(-1) x min(-1); P < 0.05), as well as increased insulin suppressibility of muscle total long-chain fatty acyl-CoA (LC-CoA), the metabolically available form of fatty acid (EX 24.0, GM 15.5, and NM 30.6 vs. FM 45.4 nmol/g; P < 0.05). There was a strong inverse correlation between glucose uptake and LC-CoA in red quadriceps during the clamp (r = -0.7, P = 0.001). Muscle triglyceride was significantly reduced by short-term dietary lipid withdrawal (GM -22 and NM -24% vs. FM; P < 0.01), but not prior exercise. We concluded that muscle insulin resistance induced by high-fat feeding is readily ameliorated by three independent, short-term physiological manipulations. The data suggest that insulin resistance is an important factor in the elevated muscle lipid availability induced by chronic high-fat feeding.

Contraction-induced changes in acetyl-CoA carboxylase and 5'-AMP-activated kinase in skeletal muscle

The concentration of malonyl-CoA, a negative regulator of fatty acid oxidation, diminishes acutely in contracting skeletal muscle. To determine how this occurs, the activity and properties of acetyl-CoA carboxylase beta (ACC-beta), the skeletal muscle isozyme that catalyzes malonyl-CoA formation, were examined in rat gastrocnemius-soleus muscles at rest and during contractions induced by electrical stimulation of the sciatic nerve. To avoid the problem of contamination of the muscle extract by mitochondrial carboxylases, an assay was developed in which ACC-beta was first purified by immunoprecipitation with a monoclonal antibody. ACC-beta was quantitatively recovered in the immunopellet and exhibited a high sensitivity to citrate (12-fold activation) and a Km for acetyl-CoA (120 microM) similar to that reported for ACC-beta purified by other means. After 5 min of contraction, ACC-beta activity was decreased by 90% despite an apparent increase in the cytosolic concentration of citrate, a positive regulator of ACC. SDS-polyacrylamide gel electrophoresis of both homogenates and immunopellets from these muscles showed a decrease in the electrophoretic mobility of ACC, suggesting that phosphorylation could account for the decrease in ACC activity. In keeping with this notion, citrate activation of ACC purified from contracting muscle was markedly depressed. In addition, homogenization of the muscles in a buffer free of phosphatase inhibitors and containing the phosphatase activators glutamate and MgCl2 or treatment of immunoprecipitated ACC-beta with purified protein phosphatase 2A abolished the decreases in both ACC-beta activity and electrophoretic mobility caused by contraction. The rapid decrease in ACC-beta activity after the onset of contractions (50% by 20 s) and its slow restoration to initial values during recovery (60-90 min) were paralleled temporally by reciprocal changes in the activity of the alpha2 but not the alpha1 isoform of 5'-AMP-activated protein kinase (AMPK). In conclusion, the results suggest that the decrease in ACC activity during muscle contraction is caused by an increase in its phosphorylation, most probably due, at least in part, to activation of the alpha2 isoform of AMPK. They also suggest a dual mechanism for ACC regulation in muscle in which inhibition by phosphorylation takes precedence over activation by citrate. These alterations in ACC and AMPK activity, by diminishing the concentration of malonyl-CoA, could be responsible for the increase in fatty acid oxidation observed in skeletal muscle during exercise.

Malonyl-CoA regulation in skeletal muscle: its link to cell citrate and the glucose-fatty acid cycle

Malonyl-CoA is an inhibitor of carnitine palmitoyltransferase I, the enzyme that controls the oxidation of fatty acids by regulating their transfer into the mitochondria. Despite this, knowledge of how malonyl-CoA levels are regulated in skeletal muscle, the major site of fatty acid oxidation, is limited. Two- to fivefold increases in malonyl-CoA occur in rat soleus muscles incubated with glucose or glucose plus insulin for 20 min [Saha, A. K., T. G. Kurowski, and N. B. Ruderman. Am. J. Physiol. 269 (Endocrinol. Metab. 32): E283-E289, 1995]. In addition, as reported here, acetoacetate in the presence of glucose increases malonyl-CoA levels in the incubated soleus. The increases in malonyl-CoA in all of these situations correlated closely with increases in the concentration of citrate (r2 = 0.64) and to an even greater extent the sum of citrate plus malate (r2 = 0.90), an antiporter for citrate efflux from the mitochondria. Where measured, no increase in the activity of acetyl-CoA carboxylase (ACC) was found. Inhibition of ATP citrate lyase with hydroxycitrate markedly diminished the increases in malonyl-CoA in these muscles, indicating that citrate was the major substrate for the malonyl-CoA precursor, cytosolic acetyl-CoA. Studies with enzyme purified by immunoprecipitation indicated that the observed increases in citrate could have also allosterically activated ACC. The results suggest that in the presence of glucose, insulin and acetoacetate acutely increase malonyl-CoA levels in the incubated soleus by increasing the cytosolic concentration of citrate. This novel mechanism could complement the glucose-fatty acid cycle in determining how muscle chooses its fuels. It could also provide a means by which glucose acutely modulates signal transduction in muscle and other cells (e.g., the pancreatic beta-cell) in which its metabolism is determined by substrate availability.

Malonyl coenzyme A and adiposity in the Dahl salt-sensitive rat: effects of pioglitazone

These studies were designed to assess the effects of pioglitazone, a new oral antidiabetic agent that acts by improving insulin sensitivity, on blood pressure, plasma and tissue lipids, and insulin resistance in the Dahl salt-sensitive (Dahl-S) rat. Reaven et al had reported that male Dahl-S rats are moderately hyperinsulinemic and insulin-resistant. This was of particular interest since these rats are not obese but are hypertriglyceridemic, and on a high-salt diet they become hypertensive. In the current study, male Sprague-Dawley control and Dahl-S rats were compared when fed standard chow of high-fat, high-sucrose (HFHS) diets with or without pioglitazone (20 mg/kg body weight/d) for 3 weeks. On the standard chow diet, Dahl-S rats were hypertriglyceridemic and had high tissue levels of malonyl coenzyme A ([CoA] Dahl-S 5.0 v control 3.3 nmol/g in muscle, and Dahl-S 15.6 v control 10.7 nmol/g in liver); however, they were not hyperinsulinemic. Pioglitazone therapy decreased both malonyl CoA and plasma triglycerides toward control values, but had no effect on plasma insulin levels. On the HFHS diet, both groups became glucose-intolerant and hyperinsulinemic; however, the hyperinsulinemia was greater and more sustained in Dahl-S rats. In addition, the HFHS diet appeared to increase the mass of retroperitoneal fat in the Dahl-S but not in the control group. Treatment with pioglitazone decreased retroperitoneal fat, but as reported previously, it increased the mass of the epididymal fat pad. The results suggest that the hypertriglyceridemia of the Dahl-S rat is associated with an increase in the concentration of malonyl CoA in both liver and muscle. They also show that pioglitazone reverses both of these abnormalities independently of its effect on plasma insulin. Whether these high levels of malonyl CoA predispose the Dahl-S rat to hyperinsulinemia and possibly obesity when placed on a HFHS diet remains to be determined.

Smoking habits and respiratory symptoms: observations among college students and professionals

The study comprising smoking habits among educationally and socially forward class, its impact on respiratory system and response of the said class of people to a questionnaire was undertaken among a random sample of 1188 subjects consisting of students and professionals aged between 15 and 65 years. Results showed that smoking habit was alarmingly high (48.8%) among the students and a little higher (53%) among the professionals. The exact nature and extent of the problem of smoking was not very much clear to all the subjects.

A malonyl-CoA fuel-sensing mechanism in muscle: effects of insulin, glucose, and denervation

Increases in the concentration of malonyl-CoA in skeletal muscle have been observed in the KKAy mouse, an obese rodent with high plasma insulin and glucose levels [Saha et al. Am. J. Physiol. 267 (Endocrinol. Metab. 30): E95-E101, 1994]. To assess whether insulin and glucose directly regulate malonyl-CoA in muscle, soleus muscles from young rats were incubated with insulin and glucose at various concentrations, and their content of malonyl-CoA was determined. In addition, the effect on malonyl-CoA of denervation and electrically induced muscle contractions was assessed. The concentration of malonyl-CoA in the soleus, taken directly from a rat fed ad libitum, was 2.0 +/- 0.2 nmol/g. In muscles incubated for 20 min in a medium devoid of added insulin and glucose, the concentration was decreased to 0.8 +/- 0.2 nmol/g. When the medium contained 0.5, 7.5, or 30 mM glucose, malonyl-CoA levels were 1.3 +/- 0.1, 1.8 +/- 0.1, or 2.4 +/- 0.2 nmol/g, respectively, in the absence of insulin and 1.7 +/- 0.1, 4.6 +/- 0.3, or 5.5 +/- 0.6 nmol/g in its presence (10 mU/ml). Compared with its level in a control muscle, the concentration of malonyl-CoA was increased threefold in the soleus 6-8 h after denervation and remained twofold higher for > or = 48 h. In contrast, muscle contractions induced by sciatic nerve stimulation, in vivo, acutely decreased the concentration of malonyl-CoA by 30-35%. The results indicate that insulin and glucose, and probably contractile activity, regulate the concentration of malonyl-CoA in muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid abnormalities in tissues of the KKAy mouse: effects of pioglitazone on malonyl-CoA and diacylglycerol

Insulin resistance is present in liver and muscle of subjects with type 2 diabetes and obesity. Recent studies suggest that such insulin resistance could be related to abnormalities in lipid-mediated signal transduction; however, the nature of these abnormalities is unclear. To examine this question further, tissue levels of diacylglycerol (DAG), malonyl-CoA, and triglyceride (TG) were determined in liver and soleus muscle of obese insulin-resistant KKAy mice and lean C57 BL control mice. In addition, the effects of treatment with pioglitazone, an antidiabetic agent that acts by increasing insulin sensitivity in muscle, liver, and other tissues, were assessed. The KKAy mice were hyperglycemic (407 vs. 138 mg/dl), hypertriglyceridemic (337 vs. 109 mg/dl), hyperinsulinemic (631 vs. 15 mU/ml), and weighed more (42 vs. 35 g) than the control mice. They also had 1.5- to 2.0-fold higher levels of malonyl-CoA in both liver and muscle, higher DAG (twofold) and TG (1.3-fold) levels in muscle, and higher TG (threefold), but not DAG, levels. Treatment of the KKAy mice with pioglitazone for 4 days decreased plasma glucose, TGs, and insulin by approximately 50% and restored hepatic and muscle malonyl-CoA levels to control values. In contrast, pioglitazone increased hepatic and muscle DAG levels two- or threefold. It has no effect on muscle or hepatic TG content, and it slightly increased hepatic TGs in the control group. The results indicate that abnormalities in tissue lipids occur in both liver and muscle of the KKAy mouse and that they are differentially altered when insulin sensitivity is enhanced by treatment with pioglitazone.(ABSTRACT TRUNCATED AT 250 WORDS)

Virulence factors of the family Legionellaceae

Whereas bacteria in the genus Legionella have emerged as relatively frequent causes of pneumonia, the mechanisms underlying their pathogenicity are obscure. The legionellae are facultative intracellular pathogens which multiply within the phagosome of mononuclear phagocytes and are not killed efficiently by polymorphonuclear leukocytes. The functional defects that might permit the intracellular survival of the legionellae have remained an enigma until recently. Phagosome-lysosome fusion is inhibited by a single strain (Philadelphia 1) of Legionella pneumophila serogroup 1, but not by other strains of L. pneumophila or other species. It has been found that following the ingestion of Legionella organisms, the subsequent activation of neutrophils and monocytes in response to both soluble and particulate stimuli is profoundly impaired and the bactericidal activity of these cells is attenuated, suggesting that Legionella bacterial cell-associated factors have an inhibitory effect on phagocyte activation. Two factors elaborated by the legionellae which inhibit phagocyte activation have been described. First, the Legionella (cyto)toxin blocks neutrophil oxidative metabolism in response to various agonists by an unknown mechanism. Second, L. micdadei bacterial cells contain a phosphatase which blocks superoxide anion production by stimulated neutrophils. The Legionella phosphatase disrupts the formation of critical intracellular second messengers in neutrophils. In addition to the toxin and phosphatase, several other moieties that may serve as virulence factors by promoting cell invasion or intracellular survival and multiplication are elaborated by the legionellae. Molecular biological studies show that a cell surface protein named Mip is necessary for the efficient invasion of monocytes. A possible role for a Legionella phospholipase C as a virulence factor is still largely theoretical. L. micdadei contains an unusual protein kinase which catalyzes the phosphorylation of eukaryotic substrates, including phosphatidylinositol and tubulin. Since the phosphorylation of either phosphatidylinositol or tubulin might compromise phagocyte activation and bactericidal functions, this enzyme may well be a virulence factor. Administration of the L. pneumophila exoprotease induces lesions resembling those of Legionella pneumonia and kills guinea pigs, suggesting that this protein plays a role in the pathogenesis of legionellosis. However, recent work with a genetically engineered strain has convincingly shown that the protease is not necessary for intracellular survival or virulence. As might be expected with a complex process like intracellular parasitism, it appears that the capability of Legionella strains to invade and multiply in host phagocytes is multifactorial and that no single moiety which is responsible for the virulence phenotype will be found.

Hypertensive primary intraventricular haemorrhage

A case of hypertensive primary intraventricular haemorrhage is reported. The patient recovered with conservative management. To the best of our knowledge, there has been no previous report of this rare entity in Indian literature.

Inhibition of human seminal fluid and Leishmania donovani phosphatases by molybdate heteropolyanions

Inhibition of a tartrate-resistant acid phosphatase (ACP) from Leishmania donovani and the tartrate-sensitive ACP from human seminal fluid (prostatic ACP) was examined using a series of 13 molybdate-containing heteropolyanions. The heteropolyanions were divided into four groups based on the number of molybdenum atoms they contain: Group I, Mo4; Group II, Mo6-8; Group III, Mo12; Group IV, Mo18. Two of the four groups, those consisting of compounds that contain either an Mo4 unit or an Mo18 unit with a heteroatom in the central cavity, were potent inhibitors and exhibited the highest degree of selectivity against the leishmanial and seminal fluid ACPs. The inhibition of prostatic ACP by complex E2 could be completely reversed by dialysis. Little inhibition of the acid phosphatase, beta-glucuronidase, or alpha-mannosidase from human spleen was observed with complexes B' and E2. For the seminal fluid phosphatase, the Ki values obtained with arsenate and vanadate depended markedly on pH, suggesting that, unlike most other phosphatases, the conformation of the inhibitor binding site on human seminal fluid ACP is pH-dependent. Results of competition experiments performed with various inhibitor pairs indicated that complex D2 binds to the active site of prostatic ACP while complex M binds at some site on the enzyme that affects the active site. Binding of complex M also modifies the affinity of the enzyme for other inhibitors such as vanadate. The potency of several heteropolyanion complexes and their selective inhibition of pathophysiologically significant acid phosphatases indicate that these compounds may have value as tools for study of the structure and function of this class of enzyme and perhaps in the therapy of human disease.

Naegleria lovaniensis tarasca new subspecies, and the purepecha strain, a morphological variant of N. l. lovaniensis, isolated from natural thermal waters in Mexico

Amoebae were isolated from a natural thermal water source in Michoacán, Mexico, in September 1986. Two 500-ml samples were taken from pools with water at 45 degrees C and 46 degrees C and concentrated at 2,000 g for 15 min. The sediment was seeded on nonnutritive agar plates and incubated at 42 degrees C. The isolates were axenized in bactocasitone-serum medium. The identification of the isolates was based on their morphology, total protein and isoenzyme patterns by agarose isoelectric focusing, serology, fine structure, agglutination with Concanavalin A, sensitivity to trimethoprim, capacity to kill mice, and their cytopathic effect in Vero cells. The results showed several morphophysiological, biochemical and serological differences between the isolates and the type strain Aq/9/1/45D of Naegleria lovaniensis. These remarkable differences provide sufficient evidence to consider one of the isolates a new subspecies, and the other one a morphological variant of N. l. lovaniensis, which can be differentiated from other Naegleriae by their morphology, biochemistry, serology and physiology. The authors propose the name tarasca for the subspecies and purepecha for the morphological variant.

Characterization of a phosphomonoesterase from Brucella abortus

Brucellae are facultative intracellular bacterial pathogens that reside primarily in cells of the reticuloendothelial system. The high-speed supernatant obtained after centrifuging a suspension of Brucella abortus that had been frozen-thawed and sonicated contained abundant phosphomonoesterase activity, determined by using 4-methylumbelliferylphosphate as the substrate; this enzyme was purified 2,900-fold (yield, 570%) by chromatography on DE-52 cellulose and hydroxylapatite columns and high-performance liquid chromatography-gel filtration. The native enzyme had a molecular mass of 120,000 daltons (+/- 10,000 daltons), as determined by gel filtration chromatography, and resolved into two bands (60,000 and 66,000 daltons) when subjected to polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The B. abortus phosphomonoesterase had the following properties: pH optimum, 6.0 to 6.5; isoelectric point, 3.0; substrate specificity, 5'-AMP greater than 3'-AMP greater than 3'-GMP greater than 5'-GDP greater than 5'-CDP greater than 5'-CTP greater than 5'-UPT greater than phosphotyrosine greater than phosphoserine greater than phosphothreonine. The Km for 5'-AMP was 0.37 mM. Phosphatidylinositol 4,5-bisphosphate and myo-inositol 1,3,4-trisphosphate were poor substrates for the B. abortus enzyme. The phosphomonoesterase did not inhibit superoxide anion production by human neutrophils stimulated with formyl-methionyl-leucyl-phenylalanine. The phosphomonoesterase may be one of the bacterial enzymes in the pathway leading to the production of adenine, which is secreted by B. abortus and blocks the activation of neutrophils.

Heparin binds to Leishmania donovani promastigotes and inhibits protein phosphorylation

We show that promastigotes of Leishmania donovani, the causative agent of visceral leishmaniasis (kala-azar), possess heparin receptors on their surface. From a linear Scatchard plot of the binding data obtained using [3H]heparin and viable promastigotes, one derives a binding constant of 4.7 x 10(-7) M and an estimate of 860,000 receptors per parasite. The [3H]heparin bound to parasites could not be displaced by hyaluronic acid or by three other glycosaminoglycans (dermatan sulphate, chondroitin 4-sulphate and chondroitin 6-sulphate). It was demonstrated that exponential phase promastigotes growing in medium 199 supplemented with fetal bovine serum incorporate 35SO4 into a cell-associated macromolecule that has the properties of heparin proteoglycan. Heparin inhibits the activity of the cell-surface histone-protein kinase; incubation of viable promastigotes with [gamma-32P]ATP and MgCl2 (10 mM) in the absence and presence of heparin (0.01-0.5 mg/ml) for 10 min, followed by analysis by SDS/polyacrylamide-gel electrophoresis and autoradiography, revealed that the phosphorylation of 12 or 13 parasite proteins was inhibited by the glycosaminoglycan. These data suggest that heparin may play a role in the host-parasite relationship.

Vanadate monomers and dimers both inhibit the human prostatic acid phosphatase

A combination of enzyme kinetics and 51V NMR spectroscopy was used to identify the species of vanadate that inhibits acid phosphatases. Monomeric vanadate was shown to inhibit wheat germ and potato acid phosphatases. At pH 5.5, the vanadate dimer inhibits the human prostatic acid phosphatase whereas at pH 7.0 it is the vanadate monomer that inhibits this enzyme. The pH-dependent shift in the affinity of the prostatic phosphatase for vanadate is presumably due to deprotonation of an amino acid side chain in or near the binding site resulting in a conformational change in the protein. pH may be a subtle effector of the insulin-like vanadate activity in biological systems and may explain some of the differences in selectivity observed with the protein phosphatases.

Legionella micdadei protein kinase catalyzes phosphorylation of tubulin and phosphatidylinositol

Legionella micdadei, a pathogen which enters into host phagocyte phagolysosomal structures, contains at least two protein kinases. We have purified to homogeneity the predominant, nucleotide-independent protein kinase and examined its ability to catalyze the transfer of phosphate from ATP to acceptors in human neutrophils. The L. micdadei protein kinase catalyzed the phosphorylation of proteins of 11.5, 14, 19, 23, 28, 34, and 38 kilodaltons (kDa) present in a Triton X-100 extract of neutrophil membranes and of 11.5, 13.5, 25, and 38 kDa in the neutrophil cytosol. Tubulin was a good substrate for the L. micdadei protein kinase in vitro. The bacterial kinase also catalyzed the phosphorylation of phosphatidylinositol (PI) at about half the rate at which histones were phosphorylated; phosphatidylinositol-4-phosphate (PIP) was not phosphorylated by the kinase. The PI kinase activity of the L. micdadei enzyme was optimum at pH 7.0, and the divalent cation requirement was satisfied best by Mg2+ and Ca2+. The maximum rate of PI phosphorylation was obtained with 0.6 mM PI; in the presence of MgCl2 (10 mM), the Km for PI was 0.9 mM and the Km for ATP was 1.5 mM. The detergents octyl-beta-D-glucoside (10 to 20 mM) and Triton X-100 (0.5%) stimulated kinase activity twofold when PI was the phosphate acceptor; however, only octyl glucoside stimulated histone kinase activity. Various membrane phospholipids inhibited PI kinase activity. The most potent phospholipid inhibitor was the product of the PI kinase reaction, PIP, which at a 0.6 mM concentration inhibited both PI and tubulin phosphorylation by 80%. The inhibition of kinase activity by PIP when histone served as the acceptor was noncompetitive in character. The L. micdadei kinase also phosphorylated PI in intact. (3H)inositol-labeled neutrophils. The PI kinase and histone kinase activities of teh L. micdadei kinase copurified and cofucused (pI, 5.8) when subjected to isoelectric focusing, suggesting that the two enzymatic activities reside in a single protein.

Inhibition of neutrophil and natural killer cell function by human seminal fluid acid phosphatase

The major acid phosphatase of human seminal fluid was purified to homogeneity by chromatography on Sephadex G-150, and DEAE-Sephadex, and by isoelectric focusing (pI, 4.3). This purified preparation of seminal fluid acid phosphatase blocked superoxide anion production by neutrophils stimulated with fMet-Leu-Phe (fMLP) by 50%. The phosphatase also hydrolysed myo-inositol 1,4,5-trisphosphate (IP3) in vitro, an intracellular second messenger which releases Ca2+ from intracellular pools, at nearly one-third the rate at which the nonphysiologic substrate 4-methylumbelliferylphosphate (MUP) was cleaved. In contrast, two phosphoinositide lipids, namely phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 4-monophosphate, were poor phosphatase substrates. Following fMLP stimulation of [3H]inositol-labeled neutrophils, the quantity of IP3 produced by phosphatase-treated cells was reduced by 69%. These results indicate that the human seminal fluid acid phosphatase may compromise the neutrophil's microbicidal response to the organism by hydrolyzing a second messenger (IP3) which is directly involved in the regulation of intracellular Ca2+ concentrations. The seminal fluid phosphatase also inhibited by 85% the ability of murine natural killer (NK) cells to inactivate target cells.

Comparison of the protein kinase and acid phosphatase activities of five species of Leishmania

Promastigotes from log phase and stationary phase cultures of Leishmania donovani, L. braziliensis panamensis, L. tropica, L. major, and L. mexicana amazonensis were analyzed for their content of protein kinase and acid phosphatase activities. Cell surface, histone-specific protein kinase activity was 1.3- to 2.8-fold higher in stationary phase cells of all species except for L. tropica in which the activities of stationary and log phase cells were equal; L. mexicana amazonensis had the highest histone-specific protein kinase activity and L. donovani the lowest. When viable, motile promastigotes of all five species were incubated for 10 min with [gamma-32P]ATP and Mg2+ (10 mM) in the absence of exogenous histone acceptor; about one dozen proteins were phosphorylated in each case. Both log phase and stationary phase promastigotes of all five species extensively phosphorylated a 50-kDa protein that had the mobility of tubulin. Incubation of pure calf brain tubulin with [gamma-32P]ATP and purified L. donovani protein kinase resulted in extensive phosphorylation of the former. Highly infective metacyclic forms (PNA-) of L. major, isolated from a stationary culture using the peanut agglutinin (PNA), contained eight times more histone-specific protein kinase activity than noninfective log phase cells (PNA+). The PNA- and PNA+ forms of L. major both phosphorylated a 50-kDa protein when incubated with [gamma-32P]ATP and magnesium or manganese ions (10 mM); the 50-kDa protein was precipitated by anti-tubulin rabbit antibodies. Extracts of all five species contained large amounts of acid phosphatase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Legionella micdadei phosphatase catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphate in human neutrophils

The legionellae are facultative intracellular bacterial pathogens which multiply in host phagocytes. Legionella micdadei cells contain an acid phosphatase (ACP2) which blocks superoxide anion production by human neutrophils stimulated with formyl-Met-Leu-Phe (fMLP) [A. K. Saha, et al. (1985) Arch. Biochem. Biophys. 243, 150-160]. In the present study, we have purified the Legionella phosphatase to homogeneity as indicated by the finding of a single 68,000-Da band following sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We explored the possibility that ACP2 acts by interfering with polyphosphoinositide hydrolysis and the production of the intracellular second messengers, inositol trisphosphate (IP3) and diacylglycerol, following neutrophil stimulation. Phosphatidylinositol 4,5-bisphosphate (PIP2) was hydrolyzed rapidly by ACP2 in vitro. The rate of hydrolysis of PIP2 was higher at pH 7.0 (Km 2.0 microM; 4 X 10(3) units/mg protein; 1 unit equals 1 nmol of Pi released/h) than at lower pH. IP3 was also a good substrate for ACP2 in vitro. When human neutrophil phosphoinositides were prelabeled with 32Pi, subsequent incubation with ACP2 resulted in an 85% loss of the labeled PIP2 over 2 h. Following fMLP stimulation of [3H]inositol-labeled neutrophils, the quantity of IP3 produced by ACP2-treated cells was reduced by 44%. Prior treatment of neutrophils with ACP2 also reduced by 45% the amount of diacylglycerol they produced when stimulated by fMLP. These results indicate that the Legionella phosphatase may compromise the neutrophils' microbicidal response to the organism by hydrolyzing PIP2, the progenitor of IP3 and diacylglycerol, and by hydrolyzing IP3 itself.

Demonstration of two protein kinases in extracts of Legionella micdadei

Protein kinases I (PK I) and II (PK II) were purified 253- and 13.5-fold, respectively, from an extract of sonically disrupted cells of Legionella micdadei by ion-exchange chromatography on QAE-Sephadex, by histone affinity chromatography, and by HPLC-gel filtration chromatography. Both enzymes catalysed the phosphorylation of calf thymus histones, with a Km of 2.7 mg ml-1 for PK I and 2.9 mg ml-1 for PK II. Histone H2b was the best protein kinase substrate for both PK I and PK II. The pH optima were 6.8 and 7.0 for PK I and PK II respectively. The Km for ATP was 0.29 mM for PK I and 0.33 mM for PK II. PK II activity was stimulated by either cAMP or cGMP, whereas PK I was inhibited by both cyclic nucleotides. The activity of PK I was unaffected by addition of calmodulin, diacylglycerol and mixtures of Ca2+ and acidic phospholipids, but these additions increased PK II activity threefold. The activity of PK II was stimulated by spermine and spermidine, but PK I was inhibited by these compounds. PK I and PK II were both strongly inhibited by heparin.