The Mycobacterium tuberculosis Rv1099c gene encodes a GlpX-like class II fructose 1,6-bisphosphatase

There are now abundant data indicating that Mycobacterium tuberculosis uses fatty acids as a carbon source in vivo. A key enzyme in gluconeogenesis, missing in the original annotation of the M. tuberculosis genome, is fructose 1,6-bisphosphatase (FBPase; EC 3.1.3.11). The authors have shown that M. tuberculosis Rv1099c, a glpX homologue, can complement Escherichia coli mutants lacking FBPase. The protein encoded by Rv1099c was shown to have FBPase activity. Rv1099c was expressed at significant levels in M. tuberculosis, and may encode the major FBPase of this pathogen.

The decaying genome of Mycobacterium leprae

Everything that we need to know about Mycobacterium leprae, a close relative of the tubercle bacillus, is encrypted in its genome. Inspection of the 3.27 Mb genome sequence of an armadillo-derived Indian isolate of the leprosy bacillus identified 1,605 genes encoding proteins and 50 genes for stable RNA species. Comparison with the genome sequence of Mycobacterium tuberculosis revealed an extreme case of reductive evolution, since less than half of the genome contains functional genes while inactivated or pseudogenes are highly abundant. The level of gene duplication was approximately 34% and, on classification of the proteins into families, the largest functional groups were found to be involved in the metabolism and modification of fatty acids and polyketides, transport of metabolites, cell envelope synthesis and gene regulation. Reductive evolution, gene decay and genome downsizing have eliminated entire metabolic pathways, together with their regulatory circuits and accessory functions, particularly those involved in catabolism. This may explain the unusually long generation time and account for our inability to culture the leprosy bacillus.

Suppression mediated by anergic CD4+ T cells requires stimulation by MHC-peptide complexes and can be induced in the presence of costimulation

BACKGROUND

In this study, we have investigated the mechanisms involved in both the induction of suppressive anergy, the stability of the anergy induced, and the possible mechanisms by which the response of immunocompetent CD4+ T cells are suppressed.

METHODS

We used immobilized anti-CD3 monoclonal antibody (mAb) to induce anergy in T helper (Th) 1 and Th0 cells reactive with MHC class II molecule H2 I-Ab.

RESULTS

We observed that suppressive anergy was induced independently of costimulation in Th0 but not Th1 cells. Although the anergic and suppressive states of Th0 cells were stable in the presence of exogenous interleukin-2, this was not the case for Th1 cells. No evidence for linked epitope suppression was observed for any of the I-Ab reactive cells investigated. Neither anergy nor suppression was observed in Th0 cells upon restimulation with anti-CD3 in the presence of syngeneic antigen-presenting cells (APCs). However, anergy but not suppression was observed in co-cultures restimulated with anti-T-cell antigen receptor (TCR) mAbs/syngeneic APCs and suppression could be restored by the addition of I-Ab+ APCs.

CONCLUSIONS

Overall, these data suggested that the MHC-peptide complex recognized by the Th0 cells was required for suppression of the response of immunocompetent cells. We propose that suppression is mediated either by down-modulation of the MHC-peptide complex recognized by the anergic T cells or that a molecule specific to the MHC-peptide/TCR interaction facilitates negative regulation by APC:T or T:T interactions.

Massive gene decay in the leprosy bacillus

Leprosy, a chronic human neurological disease, results from infection with the obligate intracellular pathogen Mycobacterium leprae, a close relative of the tubercle bacillus. Mycobacterium leprae has the longest doubling time of all known bacteria and has thwarted every effort at culture in the laboratory. Comparing the 3.27-megabase (Mb) genome sequence of an armadillo-derived Indian isolate of the leprosy bacillus with that of Mycobacterium tuberculosis (4.41 Mb) provides clear explanations for these properties and reveals an extreme case of reductive evolution. Less than half of the genome contains functional genes but pseudogenes, with intact counterparts in M. tuberculosis, abound. Genome downsizing and the current mosaic arrangement appear to have resulted from extensive recombination events between dispersed repetitive sequences. Gene deletion and decay have eliminated many important metabolic activities including siderophore production, part of the oxidative and most of the microaerophilic and anaerobic respiratory chains, and numerous catabolic systems and their regulatory circuits.

Sulphatide-binding properties are shared by serum amyloid P component and a polyreactive germ-line IgM autoantibody, the TH3 idiotype

Serum amyloid P component (SAP) concentration was elevated in sera from leprosy patients, significantly so above endemic controls in lepromatous cases. In the sera of lepromatous leprosy (LL) patients who experienced an erythema nodosum leprosum (ENL) episode the SAP fell at the onset of ENL and remained low throughout, in two of three cases. Changes in SAP concentration parallel anti-sulphatide IgM concentrations. TH3, a monoclonal IgM germ-line antibody derived from a LL patient, and SAP share similar binding patterns. In this study we demonstrate binding to heparin and sulphatide. Moreover, SAP inhibited the binding of TH3 to sulphatide, as well as anti-sulphatide IgM found in a range of sera, and anti-sulphatide IgG in the only sera sample in which it was found. The observation that anti-TH3 idiotype monoclonal and polyclonal anti-SAP antibodies both inhibited the binding of TH3 and IgM in sera (but not IgG) to sulphatide without binding to sulphatide themselves further demonstrated similar binding specificities. The observations of similarity in binding reinforce ideas that SAP may function as a primitive opsonin, but the clear ability to inhibit binding of autoantibodies suggests that SAP may play a role in ameliorating tissue and particularly nerve damage in leprosy patients.

Determination of the primary target for isoniazid in mycobacterial mycolic acid biosynthesis with Mycobacterium aurum A+

The target of the potent antituberculosis drug isoniazid was investigated in Mycobacterium aurum A+, against which isoniazid has an MIC (the minimum concentration required to give growth inhibition) of 0.3 microgram/ml. Mycolic acid biosynthesis, measured by the incorporation of label from [1-14C]acetate into mycolic acids, was inhibited differentially by isoniazid in cell-wall preparations of M. aurum A+. Thus at an isoniazid concentration of 1 microgram/ml, mycolic acid biosynthesis was inhibited by 80% but concomitant biosynthesis of non-hydroxylated fatty acids was inhibited by only 15%. Three lines of evidence identified 24:1 cis-5 elongase as the primary isoniazid target. First, 24:1 cis-5 did not restore isoniazid-inhibited mycolic acid biosynthetic activity in a crude cell-wall preparation, suggesting that the drug acts after the formation of the delta-5 double bond. Secondly, a 24:1 cis-5 elongase assay in which the product is mycolic acid is completely inhibited by isoniazid. Finally, the only intermediates that accumulate as a result of the addition of isoniazid are acids of 24 carbons. Both 24:0 and 24:1 are observed in a similar ratio whether or not isoniazid is present, even though concomitant mycolic acid biosynthesis is inhibited by isoniazid. These results are consistent with studies of the M. tuberculosis InhA protein by Dessen, Quemard, Blanchard, Jacobs and Sacchettini [(1995) Science 267, 1638-1641].

Autoantibodies to cerebroside sulphate (sulphatide) in leprosy

Sera from 40 leprosy patients were screened for autoantibodies to cerebroside sulphate (sulphatide). Anti-sulphatide IgM in groups of patients with lepromatous (LL) and borderline (BL + BB + BT), but not with tuberculoid (TT) disease, were significantly elevated above the levels found in endemic control subjects. Eight-six percent (18 out of 21; mean 1.59 OD units) of LL, 33% (four out of 12; mean 1.08 OD units) of borderline and 13% (one out of eight; mean 0.69 OD units) of tuberculoid patients had anti-sulphatide IgM in their sera above a cut-off value of 2 s.d. above the mean value (0.66 OD units) for control sera. Elevated anti-sulphatide IgG was detected in only one patient's serum, an individual with LL disease. The level of anti-sulphatide IgM was strongly correlated to expression of the TH3 idiotype, an idiotype previously defined by a human MoAb that bound Mycobacterium leprae phenolic glycolipid, Klebsiella capsular polysaccharide, polynucleotides and human tissues. The purified, TH3 MoAb was found in this study to bind sulphatide, but not cholesterol-3-sulphate or cerebroside. It is suggested that anti-sulphatide IgM is elevated in leprosy, in relation to the bacterial load. Anti-sulphatide IgM fell at the onset of erythema nodosum leprosum (ENL) reaction, consistent with the deposition of serum antibodies, and thus may play a part in pathology during periods of inflammation, particularly in multibacillary patients.

Synthesis of methyl 3-(2-octadecylcyclopropen-1-yl)propanoate and methyl 3-(2-octadecylcyclopropen-1-yl)pentanoate and cyclopropane fatty acids as possible inhibitors of mycolic acid biosynthesis

(Z)-Tetracos-5-enoic acid is a key intermediate in the biosynthesis of myocobacterial mycolic acids. Recently the methyl ester of its cyclopropene analogue, methyl 4-(2-octadecylcyclopropen-1- yl)butanoate, was shown to act as an inhibitor of mycolic acid biosynthesis. The related analogues methyl 5-(2-octadecylcyclopropen-1-yl)pentanoate and methyl 3-(2-octadecylcyclopropen-1-yl)propanoate have been synthesized, as well as the related cyclopropane esters methyl (Z)-4-(2-octadecylcyclopropan-1-yl)butanoate and methyl (Z)-5-(2-octadecylcyclopropan-1-yl)pentanoate. The synthesis of methyl 3-(2-octadecylcyclopropen-1-yl)propanoate involved protection of the cyclopropene ring by iodination to allow oxidation of an alcohol to a carboxylic acid; the diiodocyclopropane was deprotected by a new mild procedure using activated zinc.

Lipid synthesis in mycobacteria: characterization of the biotin carboxyl carrier protein genes from Mycobacterium leprae and M. tuberculosis

The causative agents of leprosy and tuberculosis, Mycobacterium leprae and Mycobacterium tuberculosis, have a lipid-rich cell envelope which contributes to virulence and antibiotic resistance. Acyl coenzyme A carboxylase, which catalyzes the first committed step of lipid biosynthesis, consists in mycobacteria of two subunits, one of which is biotinylated. Genes from M. leprae and M. tuberculosis encoding a biotinylated protein have been cloned and sequenced. Analysis of the derived protein sequences demonstrated the presence of biotin-binding sites and putative ATP-bicarbonate interactions sites, consistent with the proteins having a biotin carboxylase function as well as their being biotin carrier proteins.

Synthesis of methyl (Z)-tetracos-5-enoate and both enantiomers of ethyl (E)-6-methyltetracos-4-enoate: possible intermediates in the biosynthesis of mycolic acids in mycobacteria

The high molecular weight 2-alkyl-3-hydroxy mycolic acids are key structural components of the cell envelope of pathogenic mycobacteria, such as Mycobacterium tuberculosis. A prime target for action would be the initial stages where the biosynthetic pathways diverge from those of ordinary fatty acids. It has been postulated that the pathway for the alpha-mycolates, without oxygen functions in addition to the hydroxy-acid unit, appears to diverge from (Z)-tetracos-5-enoic acid. The biosynthesis of oxygenated mycolic acids is considered to possibly diverge from (E)-6-(R)-methyltetracos-4-enoic and (E)-6-(S)-methyltetracos-4-enoic acids. This communication describes the synthesis of esters of these acids in order to test their potential role in the biosynthesis of mycolic acids.

Stimulation of mycolic acid biosynthesis by incorporation of cis-tetracos-5-enoic acid in a cell-wall preparation from Mycobacterium smegmatis

Mycolic acids are high molecular weight hydroxy fatty acids which are a covalently linked part of the cell wall structure of all mycobacteria and their biosynthetic pathways offer potential drug targets. Three good candidates, cis-tetracos-5-enoic acid and R or S trans-6-methyl-tetracos-4-enoic acids, for the key initial intermediates where mycolic acid biosynthesis might diverge from other metabolic pathways, were tested as possible substrates. A cell-wall preparation from Mycobacterium smegmatis, capable of mycolic acid synthesis, was developed to investigate the possible incorporation of these, and other 16 to 24 carbon acids into mycolic acids. The wall preparations were extracted with hexane and suspended in hexane/water (7:1, v/v), and in this low-water assay, only one of these acids, cis-tetracos-5-enoic acid, stimulated the incorporation of radioactive label from [1-14C]acetate into alpha- and alpha'-mycolic acids. The extraction method used did, however, abolish some enzyme activity and mycolic acid biosynthesis was not completely restored by cis-tetracos-5-enoate. The two methyl-branched acids did not enhance the amount of label in epoxymycolic acids. An initial key intermediate in the synthesis of alpha- and alpha'-mycolic acids has therefore been positively identified for the first time; intermediates in the initial stages of the biosynthesis of oxygenated mycolic acids such as epoxymycolates remain to be defined.

Control and location of acyl-hydrolysing phospholipase activity in pathogenic mycobacteria

Phospholipase activities releasing fatty acyl moieties from phosphatidylcholine and phosphatidylethanolamine and lysophospholipase activity releasing fatty acid from lyso-phosphatidylcholine were detected in both Mycobacterium microti and Mycobacterium avium. Fatty acyl groups were released from both the 1- and 2-positions of phosphatidylcholine. Generally, phospholipase activities of M. avium were cryptic while phospholipase activities of M. microti were located on the bacterial surface. However, intact M. microti did not release fatty acids from phospholipids faster than M. avium. Neither Mycobacterium secreted acyl-hydrolysing phospholipase activity. All phospholipase activities were stimulated by including phospholipids in growth media: generally, cell extracts contained 6- to 15-fold higher specific activities than extracts from mycobacteria grown in media without added phospholipid. However, not all phospholipase activities were stimulated to the same degree in any given set of conditions, suggesting the existence of more than one phospholipase gene in each Mycobacterium.

Control of acyl-CoA carboxylase activity in mycobacteria

Acyl-CoA carboxylase activity in four pathogenic mycobacteria and Mycobacterium smegmatis was shown with both acetyl-CoA and propionyl-CoA substrates. Only very low activity was detected in mycobacteria grown in host tissues or on egg-based media rich in lecithin and avidin. This appeared to be a result of severe depression of activity, as strains which could be grown both in host tissue and egg-based media, and in the relatively simple Dubos or Sauton's media showed 8 to 120-fold higher activity in the simpler media.

Phospholipase activity of Mycobacterium leprae harvested from experimentally infected armadillo tissue

Three types of phospholipase activity--phospholipase A1, A2, and lysophospholipase--were detected in Mycobacterium leprae harvested from armadillo tissue at about 25% of the specific activity found in a slowly growing mycobacterium, Mycobacterium microti, which was grown in medium to optimize its phospholipase activity. The highest activity found was lysophospholipase, which released fatty acid from 2-lyso-phosphatidylcholine. Phospholipase activity was detected by using phosphatidylcholine and phosphatidylethanolamine. Differences in relative activities with these three types of substrate distinguished phospholipase activity in M. leprae extracts from armadillo liver extracts. Furthermore, retention of activity in M. leprae after NaOH treatment showed that the activity associated with M. leprae was not host derived. The specific activity of phospholipase was 20 times higher in extracts of M. leprae than in intact M. leprae organisms. Diazotization, a treatment which abolishes activities of surface enzymes exposed to the environment by the formation of covalent azide bonds with exposed amino groups, did not affect M. leprae's phospholipase activity, with one exception: release of arachidonic acid from phosphatidylcholine, which was partially inhibited. Phenolic glycolipid I, the major excreted amphipathic lipid of M. leprae, inhibited phospholipase activity, including release of arachidonic acid, for both M. leprae- and armadillo-derived activity.

Fatty acid oxidation and the beta-oxidation complex in Mycobacterium leprae and two axenically cultivable mycobacteria that are pathogens

Intact, non-growing Mycobacterium leprae, M. avium and M. microti oxidized a wide range of 1-14C-labelled fatty acids (C8 to C24) to 14CO2. Laurate (C12) was oxidized most rapidly, and its oxidation by M. leprae was inhibited by the antileprosy agents Dapsone, clofazamine and rifampicin. Key enzymes of beta-oxidation were detected in extracts from all three mycobacteria. All these activities (both in intact mycobacteria and the enzymes) were stimulated in M. avium grown in Dubos medium plus palmitate but activities in M. microti or M. avium grown either in Dubos medium with added liposomes or triolein, or in vivo were similar to those detected in the same strain grown in Dubos medium alone. M. avium could be grown in medium in which 95% of its fatty acyl elongase activity is acetyl-CoA dependent. In this medium growing M. avium organisms oxidized [1-14C]palmitate to 14CO2 but simultaneously elongated palmitate to C24 acids and even longer. Acetyl-CoA-dependent elongase activity is similar but clearly not identical to reversed beta-oxidation, but the exact point(s) of difference have not yet been identified.

Aspartate metabolism in Mycobacterium avium grown in host tissue and axenically and in Mycobacterium leprae

Aspartokinase activity was detected in extracts from Mycobacterium leprae (recovered from armadillo liver) and in Mycobacterium avium grown axenically and in vivo. Homoserine dehydrogenase activity was only detected in M. leprae and in M. avium grown axenically. Activities, when detected, were 50 to 70% lower in M. leprae or M. avium grown in vivo than in axenically grown M. avium. In these two pathogenic mycobacteria, aspartokinase and homoserine dehydrogenase are subject to feedback inhibition by methionine - an additional regulator over those observed for the enzymes from Mycobacterium smegmatis. Intact mycobacterium incorporated carbon from [U-14C]aspartate into the aspartate family of amino acids (threonine, isoleucine, methionine and lysine) though the rate of incorporation in M. avium grown in vivo was about half that in M. avium grown axenically.

Enzymes for biosynthesis de novo and elongation of fatty acids in mycobacteria grown in host cells: is Mycobacterium leprae competent in fatty acid biosynthesis?

Fatty acid synthetase activity in extracts of Mycobacterium leprae was equivalent to 1.7 pmol malonyl-CoA incorporated into fatty acid min-1 (mg protein)-1. This activity--if representative of living M. leprae organisms--is insufficient to enable them to synthesize their lipid requirements rapidly enough to support growth. The major activity for scavenging fatty acids in extracts of Mycobacterium microti and Mycobacterium avium, as well as in extracts of M. leprae, was acetyl-CoA-dependent fatty acyl-CoA 'elongase'. This activity was about four times higher in M. avium and M. microti grown in a medium which contained lipids, or when grown in mice, than in medium without added lipids. In contrast, the de novo fatty acid synthetase activity was repressed in M. avium and M. microti when grown in medium that contained lipids, or when grown in mice. These results are consistent with the hypothesis that mycobacteria grown in vivo preferentially scavenge lipids from the host cells, and suggest that a source of lipid should be included in media for attempted axenic isolation of M. leprae.

Biosynthesis and scavenging of pyrimidines by pathogenic mycobacteria

Mycobacterium microti incorporated a wide range of exogenously supplied pyrimidines into its nucleic acids. M. avium incorporated a relatively narrow range of pyrimidines but both M. avium and M. microti when recovered after growth in vivo incorporated a slightly wider range of pyrimidines than the same strains grown in vitro. M. microti and M. leprae could not take up uridine nucleotides directly but could utilize the pyrimidines by hydrolysing them to uridine and then taking up the uridine. Pyrimidine biosynthesis, judged by the ability to incorporate carbon from CO2 or aspartate into pyrimidines was readily detected in non-growing suspensions of M. microti and M. avium harvested from Dubos medium, which does not contain pyrimidines. The biosynthetic activity was diminished in mycobacteria grown in vivo when there is likely to be a source of pyrimidines which they might use. Relative activities for pyrimidine biosynthesis de novo in M. microti were 100 for cells isolated from Dubos medium, 6 for cells isolated from Dubos medium containing the pyrimidine cytidine and 11 from cells recovered after growth in mice. In contrast, relative activities for a scavenging reaction, uracil incorporation, were 100, 71 and 59, respectively. Three key enzymes in the pathway of pyrimidine biosynthesis de novo were detected in M. microti and M. avium. Two, dihydroorotate synthase and orotate phosphoribosyltransferase appeared to be constitutive in M. microti and M. avium. Aspartate transcarbamoylase activity was higher in these mycobacteria grown in vivo than in Dubos medium but it was repressed in M. microti or M. avium grown in Dubos medium in the presence of 50 microM-pyrimidine. Aspartate transcarbamoylase was strongly inhibited by the feedback inhibitors ATP, CTP and UTP. Enzymes for scavenging pyrimidines were detected at low specific activities in all mycobacteria studied. Activities of phosphoribosyltransferases, enzymes that convert bases directly to nucleotides, were not related to the ability of intact mycobacteria to take up pyrimidine bases while activities of pyrimidine nucleoside kinases were generally related to the ability of intact mycobacteria to take up nucleosides. Phosphoribosyltransferase activity for uracil, cytosine, orotic acid and--in organisms grown in Dubos medium with 50 microM-uridine-thymine, as well as kinases for uridine, deoxyuridine, cytidine and thymidine were detected in M. microti. However, M. avium only contained uracil and orotate phosphoribosyltransferase, uridine, cytidine and thymidine kinase, and additionally deoxyuridine kinase when grown axenically with 50 microM-uracil, reflecting its more limited abilities in pyrimidine scavenging.

Metabolism of aspartate in Mycobacterium smegmatis

Mycobacterium smegmatis grows best on L-asparagine as a sole nitrogen source; this was confirmed. [14C]Aspartate was taken up rapidly (46 nmol.mg dry cells-1.h-1 from 1 mM L-asparagine) and metabolised to CO2 as well as to amino acids synthesised through the aspartate pathway. Proportionately more radioactivity appeared in the amino acids in bacteria grown in medium containing low nitrogen. Activities of aspartokinase and homoserine dehydrogenase, the initial enzymes of the aspartate pathway, were carried by separate proteins. Aspartokinase was purified as three isoenzymes and represented up to 8% of the soluble protein of M. smegmatis. All three isoenzymes contained molecular mass subunits of 50 kDa and 11 kDa which showed no activity individually; full enzyme activity was recovered on pooling the subunits. Km values for aspartate were: aspartokinases I and III, 2.4 mM; aspartokinase II, 6.4 mM. Aspartokinase I was inhibited by threonine and homoserine and aspartokinase III by lysine, but aspartokinase II was not inhibited by any amino acids. Aspartokinase activity was repressed by methionine and lysine with a small residue of activity attributable to unrepressed aspartokinase I. Homoserine dehydrogenase activity was 96% inhibited by 2 mM threonine; isoleucine, cysteine and valine had lesser effects and in combination gave additive inhibition. Homoserine dehydrogenase was repressed by threonine and leucine. Only amino acids synthesised through the aspartate pathway were tested for inhibition and repression. Of these, only one, meso-diaminopimilate, had no discernable effect on either enzyme activity.

Pyrimidine scavenging by Mycobacterium leprae

Mycobacterium leprae incorporated exogenously supplied pyrimidines as bases or nucleosides, but not as a nucleotide, into its nucleic acids. Notably, thymine was incorporated approximately 5 times more rapidly than thymidine by both suspensions of, or intracellular M. leprae. Thymine incorporation was significantly inhibited by clofazamine and dapsone at near-pharmacological levels. Therefore, incorporation of thymine is preferable as an activity for assessing viability of M. leprae. Nucleosides were converted to nucleotides through kinases, bases through phosphoribosyltransferases. Alternatively, thymine and uracil could first be converted to nucleosides. Cytosine and uracil bases were interconvertible, and uracil alone could supply all the pyrimidine requirements of M. leprae, though conversion to the thymine base was extremely slow. Overall, pyrimidine scavenging occurs at a slower rate than, and appears not to be so important as purine scavenging in M. leprae.

Pyrimidine biosynthesis de novo in M. leprae

Mycobacterium leprae can synthesise pyrimidines de novo. Although pyrimidine synthesis could not be detected in intact bacteria, extracts contained all four enzymes unique to the de novo pathway which are detectable in mycobacteria by the methods used. Inhibition of aspartate transcarbamylase by UTP and ATP suggested that lack of pyrimidine synthetic activity in whole M. leprae could be a result of strong feedback inhibition.

Use of carbon sources for lipid biosynthesis in Mycobacterium leprae: a comparison with other pathogenic mycobacteria

Carbon from glycerol and palmitate, but not significantly from five other carbon sources tested, was incorporated into lipids by suspensions of non-growing Mycobacterium leprae organisms. However, of the five other substrates three-citrate, glucose and pyruvate-were taken up. Nongrowing Mycobacterium microti and Mycobacterium avium incorporated carbon into lipids from most simple carbon sources tested unless they were obtained from growth media including palmitate or from experimentally infected animals, when incorporation of carbon into lipids from carbon sources except palmitate occurred up to 20 times more slowly. Thus, utilization of simple carbon appeared to be repressible while utilization of the one fatty acid tested, palmitate, appeared constitutive. In M. leprae, carbon from glycerol was incorporated into the glycerol moiety of acylglycerols but not into the fatty acid moieties or into free fatty acids. M. microti and M. avium incorporated carbon from simple carbon sources into fatty acids, even (though very slowly) when these organisms were obtained from host tissue. Isocitrate lyase, malate synthase and acetate kinase were detected in M. leprae. However acetyl-CoA synthetase was not detectable and phosphoacetylase was deficient; thus, M. leprae may be incapable of making acetyl-CoA from acetate. Phosphotransacetylase was readily detected in both host-grown M. avium and M. microti.

Measurement of hypoxanthine incorporation in purified suspensions of Mycobacterium leprae: a suitable method to screen for anti-leprosy agents in vitro

The rate of incorporation of hypoxanthine was measured in suspensions of Mycobacterium leprae, with and without added anti-leprosy agents. Dapsone, clofazamine and brodimoprim, as well as other benzylpryimidines, inhibited hypoxanthine incorporation, and their minimum inhibitory concentrations for incorporation with intact M. leprae were near the minimum inhibitory concentrations at which the agents have antibacterial effects. At sub-inhibitory concentrations for hypoxanthine incorporation, some combinations of benzylpyrimidines and dapsone were inhibitory, suggesting that synergic effects of anti-leprosy agents might also be detected by the inhibition of hypoxanthine incorporation. Thus, demonstration of inhibition of hypoxanthine incorporation in M. leprae could be a rapid method for screening anti-leprosy agents and especially for preliminary testing of new, potential anti-leprosy agents. The rate of hypoxanthine incorporation was generally lower in suspensions of M. leprae with lower viability, but it was not proportional to viability so the technique would not be suitable for accurate determination of viability.

Enzymes for purine synthesis and scavenging in pathogenic mycobacteria and their distribution in Mycobacterium leprae

Three enzymes catalysing the synthesis of four intermediates (phosphoribosylglycinamide, phosphoribosylaminoimidazole-succinocarboxamide, phosphoribosylaminoimidazole-carboxamide and AMP) in the purine biosynthetic pathway were detected in extracts of Mycobacterium microti and M. avium, even when the organisms had been grown in mice. However only one of the three enzymes, adenylosuccinate AMP-lyase (catalysing the synthesis of the last two of the four intermediates listed above) was detected in M. leprae. Phosphoribosyltransferases, which convert adenine, guanine and hypoxanthine to the corresponding nucleoside monophosphates, and adenosine kinase were the major enzymes for purine scavenging in all mycobacteria studied. In contrast to enzymes in the synthetic pathway, evidence for metabolic regulation of the purine-scavenging enzymes was obtained. In particular, 20-80-fold differences in the activities of guanine phosphoribosyltransferase and adenosine kinase were observed when M. microti was grown in media with or without purines, or in mice. In M. leprae, activities of all phosphoribosyltransferases were low in comparison with activities in M. microti and M. avium (specific activity less than 2% when comparisons were made between extracts of host-grown mycobacteria). However, activity of adenosine kinase was higher in host-grown M. leprae than in host-grown M. microti or M. avium.

Biosynthesis and scavenging of purines by pathogenic mycobacteria including Mycobacterium leprae

Purine biosynthesis de novo could not be detected in suspensions of Mycobacterium leprae isolated from armadillo tissue. In contrast, non-growing suspensions of other pathogenic mycobacteria, also isolated from infected host tissue did synthesize purines. Rates of synthesis, judged by incorporation of [2-14C]glycine or [3-14C]serine into nucleic acid purines were 600 times higher in M. microti and 110 times higher in M. avium--both isolated from infected mouse tissue--than the lowest possible rate detectable and therefore the highest possible rate in M. leprae. The rate of purine synthesis relative to purine scavenging (judged by comparing incorporation of [3-14C]serine and [8-14C]hypoxanthine into nucleic acid purines in suspensions of mycobacteria) varied only slightly--4-fold in M. microti and 6-fold in M. avium--whether organisms were harvested from media with or without purines, from media with a low nitrogen content but containing a purine, from mice or even with starved organisms. Thus, the failure of M. leprae to synthesize purines could not be explained as either a result of using non-growing mycobacteria in the incubations with 14C-labelled precursors or as repression or inhibition of synthesis de novo. It appears that M. leprae requires a supply of the purine ring from its environment. Nucleotides, which may be the major source of the purine ring in the intracellular environment, were not taken up directly by M. leprae but could be hydrolysed first to nucleosides and then taken up.

Effect of homoserine on growth of Mycobacterium smegmatis: inhibition of glutamate transport by homoserine

Homoserine strongly inhibited growth of Mycobacterium smegmatis in medium containing glutamate as the sole source of nitrogen but was without effect when asparagine, alanine or glutamine was the sole nitrogen source. It was readily taken up by glutamate-grown cells, reaching an intracellular concentration of over 20 mM after 4 h incubation. The primary site of action of homoserine was deduced to be the non-competitive inhibition of glutamate transport.

Lactate dehydrogenase in Mycobacterium leprae grown in armadillo liver

Lactate dehydrogenase (LDH) was detected in extracts of untreated and NaOH-treated Mycobacterium leprae. Since armadillo liver LDH isoenzymes with a similar electrophoretic mobility were shown to be considerably more sensitive to inhibition by oxamate than LDH in M. leprae extracts, it was confirmed that M. leprae grown in armadillo liver has its own LDH. Neither the activity of LDH in M. leprae nor its electrophoretic mobility supported the tentative suggestion that an "anomolous" LDH isoenzyme in infected skin biopsies was in fact an M. leprae-derived enzyme.

Metabolism in Mycobacterium leprae: its relation to other research on M. leprae and to aspects of metabolism in other mycobacteria and intracellular parasites

Recently, some knowledge of metabolic pathways, rather than individual enzyme activities of M. leprae, is becoming available. Ultimately this may be useful in devising culture media for M. leprae. Knowledge restricted to individual reactions may be misleading. For instance, the detection of GlcNacase and beta-glucuronidase and the subcellular localization of hyaluronic acid led to attempts to cultivate M. leprae on hyaluronic-acid based medium. Subsequent investigations suggested that there was no pathway for the breakdown of hyaluronic acid in M. leprae. The biochemical pathways for breaking down glucose and glycerol seem to be complete, and thus similar to many bacteria, but there is an unusually high level of one enzyme, 6-phosphogluconate dehydrogenase (6PGDH). Although 6-phosphogluconate is oxidized by M. leprae, and this is an unusual activity, reflecting very high levels of 6PGDH, glycerol may be a preferable energy source (on the basis of rates of oxidation by suspensions) for M. leprae in attempts to cultivate the bacterium. The utilization of 6-phosphogluconate might be important for other aspects of M. leprae metabolism not yet investigated (e.g., pentose metabolism) or it may be an adaption, not needed in vitro, to its existence in host macrophages. Alternatively, its oxidation may be a way of rapidly generating NADPH at critical times for the bacterium. Other unusual activities which have been reported are the presence of an enzyme characteristic of chemoautotrophism , completely surprising in view of the biology of M. leprae. This report needs to be confirmed--some aspects, in fact, have failed to be confirmed. o-Diphenoloxidase activity is unique, among mycobacteria, to M. leprae, but there is still doubt over whether or not it is an enzymatic activity and its function is unknown. A transpeptidase which may be involved in cell wall synthesis, recently demonstrated in M. leprae, is a typical mycobacterial enzyme. It is now known that iron could be supplied to M. leprae in potential media in the form of ferriexochelin from M. neoaurum . Two "deletions" in the metabolic processes of M. leprae have been observed. Catalase appears to be absent in M. leprae; its addition to media stimulates the growth of some organisms since peroxides form in the bacteriological media . Purine synthesis de novo occurred at a very low rate compared with purine scavenging. Whether this is an adaption to growth in vivo is not known.(ABSTRACT TRUNCATED AT 400 WORDS)

Variation of superoxide dismutase levels in extracts of Mycobacterium leprae from armadillo liver

Recent improvements in the sensitivity of assay methods for superoxide dismutase (SOD) have enabled the detection of this enzyme in 18 cell-free extracts of purified Mycobacterium leprae. By converting back to units of SOD obtained in the cytochrome c-based method previously used in work on this enzyme in mycobacteria, it was shown that extracts of M. leprae had 0.15-3.84 U SOD/mg protein (this study). A mean value of 1.31 U/mg protein was calculated. It was not possible to find any factors which could explain the very high levels in some extracts, although correlation with the period of tissue storage at -80 degrees C suggested that M. leprae in freshly killed tissue would have 1.77 U SOD/mg protein. The possibility of contamination by SODs from host and other organisms was unlikely since on gel electrophoresis extracts of M. leprae with high levels of SOD showed only a single band of activity characteristic of manganese-dependent SOD previously demonstrated.

Oxidation of carbon sources through the tricarboxylic acid cycle in Mycobacterium leprae grown in armadillo liver

All the enzymes of the tricarboxylic acid cycle have now been demonstrated in extracts of Mycobacterium leprae grown in armadillo liver. Many were also present in homogenates of host-tissue, but biochemical evidence is presented which indicates that all enzymes detected in extracts from M. leprae were authentic bacterial enzymes. Further evidence for a complete tricarboxylic acid cycle in M. leprae was obtained by first establishing that citrate could be taken up and catabolized by whole M. leprae organisms, then showing that oxidation of radioisotopically labelled pyruvate to CO2 by suspensions of M. leprae was stimulated by adding unlabelled citrate. Control of tricarboxylic acid cycle activity in M. leprae by the inactivation of fumarase by a protease is speculated upon.

Exochelin-mediated iron uptake into Mycobacterium leprae

Iron chelated to the exochelins from Mycobacterium neoaurum was taken up by a suspension of M. leprae, prepared from the liver of an infected armadillo, over 15 hr. No uptake occurred when the iron was chelated with exochelins from M. bovis BCG or M. smegmatis or to a single exochelin from M. vaccae. Uptake appeared to be by facilitated diffusion since it was not inhibited by either HgCl2, NaN3, or 2,4-dinitrophenol. This was similar to the mode of uptake of ferriexochelin into M. neoaurum itself.

Enzymes of malate oxidation in Mycobacterium leprae grown in armadillo livers

A NAD-dependent malate dehydrogenase is the principal enzyme for malate oxidation by Mycobacterium leprae, FAD-dependent malate-vitamin K reductase was detected at about 1% the level of the NAD-dependent activity. Both enzyme activities were detected in extracts from M. leprae treated with NaOH to abolish host-derived activities which might be adsorbed to the bacteria and the NAD-dependent enzyme was shown to be electrophoretically distinct from the host-tissue enzyme, thus establishing that these were both authentic bacterial enzymes. Mycobacterium leprae does not possess malic enzyme.

Catabolic pathways for glucose, glycerol and 6-phosphogluconate in Mycobacterium leprae grown in armadillo tissues

With radioisotopes, it was shown that suspensions of Mycobacterium leprae oxidized glycerol, 6-phosphogluconate, glucose, glucose 6-phosphate, and, at a low rate, gluconate, to CO2. The incubation period in these experiments was usually 20 h, but after 140 h up to five times more glucose and gluconate had been converted to CO2. Studies with differentially labelled glucose indicated that glycolysis and the hexose monophosphate pathway were used for glucose dissimilation. Key enzymes of glycolysis, the hexose monophosphate pathway and glycerol catabolism were detected in cell-free extracts from purified M. Leprae, but phosphoketolase, Entner-Doudoroff pathway activity and gluconate kinase were absent. All these enzymes were present also in host-tissue, but biochemical evidence is presented which indicates that all enzymes detected in extracts from M. leprae were authentic bacterial enzymes. Additionally, they could all be detected in extracts of M. leprae prepared by treatment with NaOH in which host enzymes adsorbed to M. leprae are inactivated.

Metabolism of carbon sources by Mycobacterium leprae: a preliminary report

Glucose was established in Mycobacterium leprae by glycolysis and the hexose monophosphate pathway (30 %)-pentose phosphate pathway. Glycerol was also catabolised to CO2 at a similar rate to glucose. Key in cell-free extracts as enzymes for M. leprae.

N-acetyl-beta-glucosaminidase, beta-glucuronidase and acid phosphatase in Mycobacterium leprae

N-Acetyl-beta-glucosaminidase, beta-glucuronidase and acid phosphatase activities were detected in cell-free extracts of Mycobacterium leprae (from armadillo liver). Extracts of bacteria which had been treated with 7-diazonaphthalene-1,3-disulphonic acid to inactivate surface enzymes retained 30-45% of the activity of the glycosidases and 15% of the activity of the acid phosphatase. When intact bacteria were treated with 1 M-NaOH, the corresponding activity in the extracts was 4--9% for the glycosidases and 7% for the acid phosphatase. Inhibition studies with lactones and the use of concanavalin A-agarose showed differences between the glycosidases in extracts of M. leprae and those of armadillo liver. Inhibition studies with vanadate using extracts from NaOH-treated bacteria and extracts of armadillo liver showed differences between the acid phosphatases. Enzymes removed from the surface of M. leprae could have been adsorbed to the surface from host tissue (i.e. lysosomal enzymes) or they could have been extracellular enzymes or associated with the bacterial membrane.

Involvement of adenosine 3':5'-cyclic monophosphate in the germination of blastospores of Candida albicans

The germination of blastospores of Candida albicans is accompanied by a rise in the intracellular concentration of adenosine 3':5'-cyclic monophosphate (cyclic AMP). Germination was induced either by peptides isolated from seminal plasma or by an amino acid mixture, and both germination and the rise in cyclic AMP required a temperature of 37 degrees C. The rise occurred during the first hour of incubation, but full germination required a temperature of 37 degrees C for 4 h. Germination and the rise in cyclic AMP, in the presence of suboptimal concentrations of inducers, were stimulated by theophylline. Pre-incubation of cells with dithiothreitol in the absence of inducers inhibited subsequent germination but not the rise in cyclic AMP. Germination and the rise in cyclic AMP were inhibited if dithiothreitol or N-succinimidyl-3-(4-hydroxyphenyl)propionate was present during the induction period.

Superoxide dismutase, peroxidatic activity and catalase in Mycobacterium leprae purified from armadillo liver

Superoxide dismutase has been identified and peroxidatic activity demonstrated in Mycobacterium leprae. The superoxide dismutase, shown indirectly to be a manganese-containing enzyme, was present at low activity in the cell-free extract. Peroxidatic activity was detected in a haemoprotein on polyacrylamide gels, but quantitative assay was not possible. Catalase, although present in a cell-free extract, appeared to be a host-derived enzyme, thus emphasizing the importance of establishing the authenticity of enzyme activities in host-derived M. leprae. The implications for the growth of M. leprae in vivo and its non-cultivability are discussed in the light of these findings.

Purification and properties of peptides which induce germination of blastospores of Candida albicans

A glycopeptide and a peptide have been isolated from bovine seminal plasma which together will induce germination of Candida albicans blastospores at 37 degrees C and in the presence of glucose and Mn2+. ¿They have molecular weights of 2000 to 3000. Both peptides contain appreciable amounts of aspartic and glutamic acids, only the glycopeptide contains threonine, lysine, histidine and arginine, while only the peptide contains proline. Acid hydrolysates are fully active in inducing germination and a mixture of aspartic acid, lysine, histidine, threonine, proline and beta-alanine can replace them. Mn2+ is not then required. Amino acid mixtures are required to be present throughout the whole period in the incubation medium for full germination to take place, but the peptides can be removed after 1 h incubation and if the cells are resuspended in a buffered glucose medium full germination occurs after a further 3 h incubation.

Soluble blue as a counterstain in the Ziehl-Neelsen procedure--A brief communication

A technique is described using soluble blue instead of the conventional methylene blue as a counterstain for the Ziehl-Neelsen procedure. This increases the intensity of blue staining of non-bacterial contaminants and is useful in monitoring the progress of purification of M. leprae from host tissue.