The sialyltransferase "sialylmotif" participates in binding the donor substrate CMP-NeuAc

All members of the sialyltransferase gene family cloned to date contain a conserved region, the "sialylmotif," consisting of 48-49 amino acids in the center of the coding sequence. To investigate the function of this motif, mutant constructs of the Gal beta 1,4GlcNAc alpha 2,6-sialyltransferase were designed by site-directed mutagenesis, replacing 11 individual conserved amino acids with alanine. Each of the mutants was expressed in COS-1 cells, and eight of these retained sialyltransferase activity, allowing comparison of their enzymatic properties with that of the wild type enzyme. Kinetic analysis showed that six of eight mutants had a 3-12-fold higher Km for the donor substrate CMP-NeuAc relative to the wild type enzyme, while the Km values for the acceptor substrate were within 0.5-1.2-fold of the wild type for all eight mutants evaluated. The Ki of the donor substrate analog CDP was also evaluated for the recombinant sialyltransferase with the Val to Ala mutation at residue 220, which produced a 6-fold increase in Km of CMP-NeuAc. A corresponding increase in Ki of 3.4-fold was observed for CDP, indicating a decreased affinity for the cytidine nucleotide. Taken together, these results suggest that the conserved sialylmotif in the sialyltransferase gene family participates in the binding of the common donor substrate, CMP-NeuAc.

Multi-input optical parallel logic processing with the shadow-casting technique

The lensless shadow-casting technique for coded pattern processing usually accommodates two inputs at a time to perform desired logical operations in parallel. A method of binary encoding is proposed that can accommodate multiple input patterns for simultaneous processing. With the proposed multiple-input encoding a carry-look-ahead technique of binary addition is developed that requires fewer processing steps than the conventional ripple-carry method. Experimental results for a few logic-processing operations are included to establish the validity of the proposed technique.

Effect of nickel(II) and tetraglycine on hydroxylation of the guanine moiety in 2'-deoxyguanosine, DNA, and nucleohistone by hydrogen peroxide

The purpose of this study was to determine whether the Ni(II)-tetraglycine complex system (NiG4) that is known to disproportionate H2O2 at pH > or = 8 can catalyze oxidation of the guanine residues in 2'-deoxyguanosine (dG), calf thymus DNA, and calf thymus nucleohistone (NH) by H2O2 at physiological pH. Incubation of dG with H2O2 in the presence of NiG4 at 37 degrees C, produced two effects: (a) formation of 8-hydroxy-2'-deoxyguanosine (8-OH-dG) and (b) decomposition of dG to 2,6-diamino-4-hydroxy-5-formamidopyrimidine and several low molecular weight unidentified products. The magnitude of both effects depended on incubation time (1-48 h), H2O2 concentration (7.5-40 mM), NiG4 concentration (0.1 or 1 mM), and pH (6.0-8.0). The effects were not detected below pH 6 and above pH 8.0. For 0.1 mM NiG4 and 7.5 mM H2O2, production of 8-OH-dG from dG (0.75 mM) during 24 h at 37 degrees C was significantly lower than from NH (1 mg/ml) or DNA (0.5 mg/ml), indicating possible specific effects that might be related to the strength of interaction of NiG4 with dG, NH, or DNA. The results indicate production of hydroxyl radical or other oxidizing species in the reaction of H2O2 with NiG4 at pH 7-8. Reactions like this may be relevant to the mechanisms of Ni(II)-mediated oxidative damage, observed in vitro and in vivo, which may contribute to the toxic and carcinogenic effects of this metal.

Probing the function(s) of active-site arginine residue in Leishmania donovani adenosine kinase

The presence of arginine at the active site of Leishmania donovani adenosine kinase was studied by chemical modification, followed by the characterization of the modified enzyme. The arginine-specific reagents phenylglyoxal (PGO), butane-2,3-dione and cyclohexane-1,2-dione all irreversibly inactivated the enzyme. In contrast, adenosine kinase from hamster liver was insensitive to these reagents. The inactivation of the enzyme by PGO followed pseudo-first-order kinetics, with a second-order rate constant of 39.2 min-1.M-1. Correlation between the stoichiometry of PGO modification and extent of inactivation indicated that modification of a single residue per molecule suffices for the loss of activity. Reactivity of the essential arginine residue towards PGO was affected by the presence of adenosine (Ado) and other competing alternative substrates, consistent with an arginine residue located proximal to the Ado-binding site. The enzyme showed an intrinsic fluorescence with an emission maximum at 340 nm when excited at 295 nm. The protein fluorescence was partially quenched on addition of Ado. PGO modification also led to significant quenching of the fluorescence. However, the fluorescence of the Ado-protected enzyme, which displayed 82% of the original activity after PGO treatment, was retained. The kinetic analyses of the partially modified enzyme showed an increase in the Km for Ado from 14 to 55 microM. Furthermore, the inability of the modified enzyme to bind to 5'-AMP-Sepharose 4B affinity column provided additional evidence that modification is attended by decrease in affinity of the enzyme for Ado. The results are consistent with the interpretation that modification of the active-site arginine residue affects activity by interfering with the binding of the substrate to the active site.

Biosynthesis of a novel 3-oxo-2-tetradecyloctadecanoate-containing phospholipid by a cell-free extract of Corynebacterium diphtheriae

We have isolated, purified, and identified by chemical analyses and mass spectrometry, a novel 3-oxo-2-tetradecyloctadecanoate (dehydrocorynomycolate)-containing phospholipid (PL-1) from the chloroform-methanol extract of Corynebacterium diphtheriae. This phospholipid was separated from all of the other known dehydrocorynomycolate and 3-hydroxy-2-tetradecyloctadecanoate (corynomycolate)-containing lipids and found to be unstable even at -20 degrees C. It was present in trace amounts as a homologous series (molecular weights of 1400 and 1404 as the methyl esters) and composed of a dehydrocorynomycolate, a phosphate group, a diacylglycerol, and an unidentified amine-containing component. Because of the complexity of these phospholipids, their complete structural determination is yet to be completed. A cell-free extract of C. diphtheriae catalyzed the incorporation of radiolabel from [14C]palmitic acid into PL-1. This incorporation was ATP-dependent, and the rate was linear with respect to both time and protein concentration. The radiolabel was incorporated primarily into the dehydrocorynomycoloyl moiety of PL-1. While avidin did not show any significant effect, cerulenin showed a marked inhibition of this reaction. Based on these results, we suggest that this dehydrocorynomycolate-containing PL-1 may be the long-sought acyl carrier-containing product of a Claisen-type condensation.

Both potential dolichol recognition sequences of hamster GlcNAc-1-phosphate transferase are necessary for normal enzyme function

A potential dolichol recognition sequence (PDRS) with the 11-residue consensus F-I/V-X-F/Y-X-X-I-P-F-X-F/Y can be found in each of five microsomal enzymes that interact with dolichol or a dolichol derivative. However, no direct evidence demonstrating a role for the PDRSs has been reported. Hamster UDP-GlcNAc:dolichol phosphate N-acetylglucosamine-1-phosphate transferase (GPT) differs from the other enzymes by having two PDRSs. Stable CHO-K1 transfectants were created that expressed elevated amounts of normal GPT, GPT with a scramble mutation at the first PDRS (nearest the amino terminus), or GPT with a triple alanine-replacement mutation at the second PDRS. The mutant enzymes had no detectable catalytic activity in vivo, but were fully capable of conferring cellular resistance to the GPT inhibitor tunicamycin. In vitro studies with membrane preparations confirmed that the mutant enzymes were catalytically inactive and also showed that their recovery in microsomes was diminished compared with normal enzyme. These data demonstrate that each PDRS of hamster GPT is necessary for normal enzyme function. The implications of these data for possible roles of the PDRSs are discussed.

Effect of carnosine homocarnosine and anserine on hydroxylation of the guanine moiety in 2'-deoxyguanosine, DNA and nucleohistone with hydrogen peroxide in the presence of nickel(II)

The oxidation of 2'-deoxyguanosine (dG) to 8-hydroxy-2'-deoxyguanosine (8-OH-dG) in free dG and the dG residues of DNA and nucleohistone with H2O2 in the presence of Ni(II) and histidyl oligopeptides, carnosine, homocarnosine and anserine was studied at physiological pH. The oxidation of free dG with H2O2 was enhanced by the oligopeptides, but not by Ni(II) alone. Much greater enhancement was produced by equimolar mixtures of Ni(II) with any of the oligopeptides or with L-histidine. In contrast, the oxidation of dG residues in DNA and nucleohistone with H2O2 was not affected by the oligopeptides, but was enhanced by Ni(II). The latter enhancement remained practically unchanged when Ni(II) was accompanied by equimolar amounts of homocarnosine or anserine, whereas carnosine tended to attenuate that enhancement. The extent of formation of 8-OH-dG in free dG depended on time and concentration of H2O2 and was highest at pH 7.4. An electron spin resonance study of the reaction mixture containing H2O2, Ni(II), carnosine, homocarnosine and/or anserine provided evidence for the generation of .OH radical in the reaction media. Although it has previously been concluded that carnosine, anserine and homocarnosine might serve as anti-oxidants, the present study does not support that conclusion and shows that these compounds may even act as pro-oxidants, especially when they are complexed with Ni(II). The results suggest that carnosine, homocarnosine and anserine, by enhancing oxidation of the free dG pool, may potentiate the carcinogenic effects of Ni(II) since the resulting 8-OH-dG can be misincorporated into DNA and thus produce a mutagenic lesion.

Active site thiol(s) in Leishmania donovani adenosine kinase: comparison with hamster enzyme and evidence for the absence of regulatory adenosine binding site

Adenosine kinase (ATP, adenosine 5'-phosphotransferase, E.C. 2.7.1.20) from Leishmania donovani, unlike adenosine kinase from other known eukaryotic sources, does not elicit an inhibitory response at high concentrations of adenosine. The mechanistic basis for this unique catalytic behavior of the parasite enzyme has been probed with the help of chemical modification and enzyme inhibition kinetics experiments. The use of cysteine-directed reagents has shown that chemical integrity of cysteinyl residues is essential for the expression of functional activity of the enzyme. Thiol group titration revealed that the enzyme contains 3 cysteine residues. However, in contrast to adenosine kinase from other sources, inactivation of the parasite enzyme could be correlated with alkylation of 2 cysteinyl residues. Adenosine, but not ATP, protected 2 thiols against -SH blocker-mediated inactivation of the enzyme. The thiol groups were shown to map at positions corresponding to approximately 16, 22, and 36 kDa sites from the protein's N-terminal end. The functions of 2 thiols at the catalytic site were functional thiol groups yielded a 'protection constant' (KpAd) of 3.4 microM, while the dissociation constant (KsAD) of the enzyme-substrate complex was 2.7 microM, hence supporting involvement of the same in both processes, namely catalysis and protection. The overall results were therefore interpreted as showing that (a) the leishmanial enzyme, in contrast to adenosine kinase from other sources, contains 2 functional thiol groups at the catalytic site; and (b) the enzyme binds adenosine exclusively through the catalytic site and as a consequence is not amenable to inhibition at high adenosine concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

An improved synthesis of trehalose 6-mono- and 6,6'-di-corynomycolates and related esters

A simplified synthesis of 6-mono- and 6,6'-di-corynomycolate esters of alpha,alpha-trehalose, and related compounds, was achieved by coupling the (hydroxyl-protected) acids to the partially trimethylsilylated sugar in the presence of dicyclohexylcarbodiimide and 4-dimethylaminopyridine. As acid reactants, (2-RS,3-RS)-3-hydroxy-2-tetradecyloctadecanoic acid (DL-corynomycolic acid) and its 2RS,3SR diastereomer were prepared from methyl palmitate by sequential Claisen condensation, reduction, chromatographic separation, and saponification. Reaction with tert-butylchlorodimethylsilane (imidazole) gave the disubstituted ether-esters, which were converted into the required 3-tert-butyldimethylsilyl ethers by partial hydrolysis. 6-Linked monocorynomycolate was obtained in excellent yield (78%) from the reaction of the RS,SR acid with the known heptakis-O-(trimethylsilyl)trehalose, and in good yield from equimolar portions of RS,RS acid and hexakis-O-(trimethylsilyl)trehalose. An excess (2.5-molar portions) of the RS,RS acid gave the 6,6'-diester (69%). The mono- and di-palmitate were similarly obtained from (Me3Si)6-trehalose. The mono (RS,RS)-(Me3Si)6-trehalose coupling product was partially resolved on a silica gel column into its RR and SS diastereomers, the former corresponding to the naturally occurring trehalose monocorynomycolate. All coupling products were deprotected to free trehalose esters by treatment first with K2CO3 in methanol, then tetrabutylammonium fluoride-trifluoracetic acid in oxolane.

Evaluation of potential aluminum chelators in vitro by aluminum solubilization ability, aluminum mobilization from transferrin and the octanol/aqueous distribution of the chelators and their complexes with aluminum

Representative amino acids, carboxylic acids, a ketone, hydroxamic acids, 3-hydroxypyridinones and a linear catecholcarboxyamide were tested in vitro to estimate their aluminum (Al) chelation potential. Their ability to solubilize Al from insoluble Al borate in a previously described octanol/aqueous (o/a) system was tested. Salicylhydroxamic acid, rhodotorulic acid, the 3-hydroxypyridin-4-ones and a sulfonated linear polycatecholcarboxamide significantly increased solubilized Al, suggesting Al chelation potential. Some of the above compounds and some compounds previously shown to solubilize Al in the o/a system were tested for their ability to mobilize Al from the Al plasma binding protein transferrin. Chelators solubilizing Al in the o/a system were comparably effective in mobilizing Al from transferrin, supporting the utility of the o/a system as a screening method. The o/a distribution coefficient of each chelator was determined, when possible, to assess its hydrophilicity. When compared with the suggested desirable hydrophilicity of effective chelators, the o/a distribution coefficient of many of the 3-hydroxypyridin-4-ones and a sulfonated linear polycatecholcarboxamide suggest that they might be able to chelate intracellular Al. The o/a distribution coefficient of each Al-chelator complex was determined, when possible, to predict the likelihood of redistribution within or excretion from the intact animal of this complex. Complexation of chelators with Al usually increased chelator hydrophilicity. The results suggest several compounds that warrant further investigation as potential alternatives to desferrioxamine in the treatment of Al accumulation and toxicity.

Mechanisms of nickel carcinogenesis. Interaction of Ni(II) with 2'-deoxynucleosides and 2'-deoxynucleotides

Interactions of Ni(II) with the base moieties of 2'-deoxynucleosides and 2'-deoxynucleotides were studied by means of UV difference spectroscopy in order to elucidate the mechanisms of site-specific enhancement by Ni(II) of DNA base oxidation with active oxygen species, observed previously (Kasprzak et al., Cancer Res., 49 (1989) 5964; Carcinogenesis, 11 (1990) 647). The interactions were generally weak and could be quantitated only at pH 7.2-7.9. The resulting coordination binding of Ni(II) was stronger with the purine derivatives, especially these of guanine, than with pyrimidine derivatives. Also, Ni(II) interacted more strongly with the bases of 2'-deoxynucleotides than with the bases of 2'-deoxynucleosides. The apparent stability constants for the interactions calculated with the use of a non-linear regression method, equalled 102 +/- 14, 159 +/- 30 and 290 +/- 70 M-1 for Ni(II) coordinated by 5'dAMP, 5'dADP and 5'dATP, respectively, and 305 +/- 73, 191 +/- 54, and 270 +/- 28 M-1 for 5'dGMP, 5'dGDP and 5'dGTP, respectively. Stability constant for the dG Ni(II) interaction was 39 +/- 7 M-1. Interactions of Ni(II) with the bases of dA, dC, dT and the dC- and dT- mono-, di- and tri-phosphates were too weak for meaningful quantitation. The strongest relative Ni(II) interaction with dG may explain high sensitivity of the dG site at the DNA molecule to Ni(II)-mediated oxidation observed in vitro and in vivo. The present results contrast with Ni(II)-directed site specific cleavage of DNA with H2O2 that occurs preferentially at the pyrimidine bases (Kawanishi et al., Carcinogenesis, 10 (1989) 2231).

Central nervous pathways underlying synchronization of human motor unit firing studied during voluntary contractions

1. Motor unit firing has been studied during weak voluntary isometric contractions with pairs of needle electrodes in normal human subjects. 2. Pre- and post-stimulus time histograms of the firing time of firing of one event unit before and after the time of firing of another reference (stimulus) unit showed a clear central peak, indicative of synchronization. 3. Synchronization was seen in all the muscles studied. The mean strength of synchronization, expressed as the number of concomitant discharges of the two units as a proportion of the number of stimulus unit discharges, was 0.095 extra event unit spikes/reference unit spike (range 0.042-0.28) for first dorsal interosseous muscle, 0.016 extra event unit spikes per reference unit spike (range 0-0.043) for medial gastrocnemius and 0.056 extra event unit spikes per reference unit spike range 0.016-0.079) for tibialis anterior. 4. The mean duration of synchronization was 11.3 ms (range 5.0-21.0 ms) for first dorsal interosseous, 10.3 ms (range 3.5-21.7 ms) for medial gastrocnemious and 13.5 ms (range 3.0-25.0) for tibialis anterior. 5. Seven patients with radiographically and clinically identified central strokes were studied while they made weak voluntary isometric contractions. The duration of synchronization was significantly prolonged compared to that found in normal subjects. In these stroke patients the mean duration of synchronization on the affected side was longer than that seen in the normal subjects, and in first dorsal interosseous muscle was 35.4 ms (range 12.0-65.0 ms), in medial gastrocnemius was 21.3 ms (range 4.0-43.0 ms) and in tibialis anterior was 28.8 ms (range 14.0-49.0 ms). 6. The mean strength of synchronization of motor unit discharge was found to be greater in the stroke patients than that seen in the normal subjects for first dorsal interosseous muscle (0.161 extra event unit spikes per reference unit spike, range 0.017-0.391) and for medial gastrocnemius (0.030 extra event unit spikes per reference unit spike) but only significantly so when pooled data was compared. There was no difference in the strength of motor unit synchronization in tibialis anterior between stroke patients and normal subjects. 7. Broad duration synchronization among first dorsal interosseous motor units was also found in a patient with a rostral cervical spine lesion (total duration range 43-46 ms; n = 2), but not in a patient with a caudal (thoracic) spinal lesion.(ABSTRACT TRUNCATED AT 400 WORDS)

The influence of induced hypocapnia and sleep on the endogenous respiratory rhythm in humans

1. Ventilation has been studied during hypocapnia produced by passive mechanical ventilation in ten normal human subjects. 2. During wakefulness, disconnection of the ventilator led to inconsistent apnoea of only brief duration. During sleep, at a similar degree of hypocapnia, disconnection of the ventilator led more consistently to apnoea which was also of much longer duration; the deeper the sleep stage, the longer the apnoea. 3. The resumption of breathing during sleep could precede or follow arousal or be unaccompanied by arousal; in the absence of prior arousal, the evidence suggests that a starting end-tidal CO2 pressure (PET, CO2) less than 41 mmHg could result in an apnoea during sleep stages I and II. 4. Subjects did not report any common sensation which led them to breathe following an apnoea whilst awake. 5. Prior hyperoxia in one subject prolonged the apnoea duration in both slow-wave sleep and rapid eye movement sleep. 6. The results are interpreted as showing that even during light sleep, the maintenance of the respiratory rhythm is critically dependent on the arterial CO2 and O2 tensions. During wakefulness, other behavioural drives, which may not reach consciousness, supervene.

New technique of arithmetic operation using the positional residue system

A simplified arithmetic digitwise positional operation is proposed that uses only moduli 2 and 5 of the residue number system.

Investigating aluminium citrate speciation by high performance liquid chromatography

The toxicity of aluminium (Al) is dependent on its chemical form or species. However, there are no current techniques available to separate small molecular weight toxic Al complexes. In the present study, HPLC separation was combined with atomic absorption spectroscopic detection of Al in an attempt to determine the potential for this analytical method to separate Al citrate from other Al species. A total of nine different HPLC stationary phase supports along with numerous mobile phases were examined. Promising results were obtained with the Cyclobond I and Cyclobond III columns containing the beta- and alpha-cyclodextrin stationary phases, respectively and the cyano column. Using a mobile phase of methanol:water (1:1; v/v) containing 0.1 M triethylamine (TEA) and glacial acetic acid (pH = 4.0), Al was reproducibly retained for approximately 9 minutes following the injection of Al citrate onto the Cyclobond III column. Injection of other simple Al complexes showed no demonstrable recovery of Al under these same conditions. However, the more stable Al desferrioxamine complex was retained, but with a retention time that was only 3-4.5 minutes. Unfortunately, the retention characteristics and recovery of Al were not reproducible or sufficient with either of the cyclobond columns for routine quantitation of Al citrate in biological samples. The cyano column did provide better recovery of Al citrate (up to 65%) than could be obtained with the cyclobond column (up to 58%). However, manipulation of the retention time for Al citrate on the cyano column was limited to a period of only 3-4.5 minutes. Under similar conditions, Al desferrioxamine could be retained for over 10 minutes on this same column.(ABSTRACT TRUNCATED AT 250 WORDS)

Synchronization of motor unit activity during voluntary contraction in man

1. Motor unit synchronization has been studied in human first dorsal interosseous muscle. 2. Two needle electrodes were inserted into the muscle and the activity of pairs of motor units recorded. 3. Pre- and post-stimulus histograms of the firing of unit pairs showed a narrow central peak of duration 1.3-9.3 ms (88% of sample in the range 1-6 ms; mode 3.0 ms), together with a variable amount of synchronization of somewhat longer duration. 4. For the duration of the whole synchronization peak (85% sample in range 5-15 ms; mode between 6.1 and 8.0 ms (31% of sample], units fired between 8 and 485% times more often than would have been expected had the units been firing independently of one another. Amplitudes of the peak of the recorded histograms expressed as a proportion of control ranged from 1.8 to 10.9 (mean 3.9; bin width 160 microseconds). 5. The strength of synchronization between the firing of motor unit pairs was inversely related to differences in recruitment threshold. The largest amount of synchronization was observed for pairs of units in which both had recruitment thresholds less than 0.5 N or greater than 1.0 N. Less synchronization was found between pairs of units in which one had a recruitment threshold less than 0.05 N and the other a threshold greater than 1.0 N. 6. The time course of synchronization was well matched by the predictions of a theoretical model based on the hypothesis that underlying the observed synchronization is the joint arrival of EPSPs from branched last-order input fibres.

Task-dependent changes in the size of response to magnetic brain stimulation in human first dorsal interosseous muscle

1. Electromyographic responses have been recorded from human first dorsal interosseous muscle (FDI) in response to magnetic and transcutaneous electrical stimulation of the brain. 2. Following magnetic but not electrical stimulation of the brain, the recorded EMG response was larger when FDI was active during voluntary isometric index finger abduction than during a power grip. 3. In the same experiment, cutaneous reflex responses have been recorded from FDI following electrical stimulation of the digital nerves. The long-latency excitatory component at about 60 ms (E2) was larger when recorded during voluntary finger abduction than during a power grip. This difference in size of E2 with task bore no simple relationship to the difference in size with task of the motor response to magnetic brain stimulation. 4. The results are discussed in relation to the presumed site of action of magnetic and electrical brain stimulation. It is concluded that the results may best be interpreted by assuming a higher level of cortical activity during a voluntary index finger abduction than during a grip and that this could in part explain the task-dependent changes in the long-latency response to cutaneous stimulation.

Effect of chemotherapy on viability of Mycobacterium leprae as determined by ATP content, morphological index and FDA-EB fluorescent staining

Viable bacterial populations were estimated in bacilli purified from 105 biopsies from 40 untreated and 65 multibacillary leprosy patients treated with multidrug therapy (MDT) for varying periods. The bacilli were purified and viability was determined by ATP content, morphological index (MI), and fluorescein diacetate-ethidium bromide (FDA-EB) staining. Viable populations were calculated, taking 3.58 x 10(-15) g/solid bacillus as the mean ATP content of a viable unit of Mycobacterium leprae. The proportion of viable bacilli was also estimated in the same specimens using solid-staining (MI) and green-staining bacilli by the FDA-EB method. In the untreated cases, the positive viability by ATP assay was 100%, 92% by MI, and 100% by FDA-EB. ATP content per solid bacillus was relatively constant, which was not the case with ATP content per green-staining bacillus. While the MI was zero in all cases, viable bacilli could still be detected by ATP estimations in 5 of the 32 (16%) patients after 2 years of MDT and in 1 of the 20 (5%) patients after 3 years of MDT. No viable bacilli could be detected even by this method beyond 3 years of MDT. On the other hand, green-staining bacilli were demonstrable in 7/32 (22%) of cases after 2 years of MDT, 2/20 (10%) after 3 years of MDT, and 1/13 (8%) after more than 3 years of treatment, indicating that the FDA-EB staining and ATP assay did not detect the same populations. A determination of the ATP content of M. leprae could be used as a reliable and sensitive tool for determining viability of the bacilli.

Epidemiological evaluation of BCG vaccine efficacy in Delhi--1989

A field evaluation of efficacy of BCG vaccine to prevent tubercular meningitis was undertaken in a case control study in Delhi during 1988-89. Each case of tubercular meningitis was matched by age and neighbourhood with 2 controls from the community. Thirty-seven cases of tubercular meningitis were matched with 74 controls and thus 37 triplets were analysed. ODDS RATIO between BCG vaccinated and non vaccinated individuals for acquisition of tubercular meningitis was 11.3. This gives 84 per cent efficacy of BCG vaccine in the prevention of TB meningitis under the field conditions prevailing in Delhi. Paired matched analysis of tubercular meningitis with the control group 1 and 2 separately revealed the ODDS RATIO to be 9.5 and 15 respectively. The corresponding BCG vaccine efficacy worked out were 90 and 93 per cent respectively. Authors suggest that this method of evaluating BCG vaccine efficacy is fairly reliable and cost effective. This methodology could be further simplified by using hospital patients as control and be introduced to evaluate BCG vaccine efficacy in different areas with reference to its role in preventing tubercular meningitis under the programme of immunisation.

Synchronization of motor unit firing during different respiratory and postural tasks in human sternocleidomastoid muscle

1. Motor unit firing has been studied in human sternocleidomastoid muscle. 2. Two needle electrodes were inserted into the muscle and the activity of pairs of motor units recorded during (a) reflex hypercapnic obstructed breathing, (b) eucapnic voluntary copying of (a) against the same inspiratory resistance and (c) voluntary copying of (a) without any resistance, accompanied by isometric neck rotation. 3. Cross-correlation histograms of the firing of unit pairs showed a clear central peak, indicative of synchronization. The mean duration of the peak during voluntary breathing was 25 ms (range 9-40 ms). There was no difference in duration of synchronization during the different tasks. 4. For the duration of the synchronization peak, the mean strength of synchronization expressed as the number of concomitant discharges of the two units as a proportion of the total number of discharges was 0.026 (range 0.011-0.058) for reflex hypercapnic obstructed breathing. For the same unit pairs the strength of synchronization for isometric neck rotation was the same as that during reflex hypercapnic breathing but for voluntary obstructed breathing it was, on average, threefold greater. 5. In three out of twenty-two motor units studied, 'discharge' occurred with an interval of less than 10 ms ('doublet' firing) at the onset of each inspiration during both types of obstructed breathing; this was rarely observed during neck rotation. 6. The results are interpreted in terms of different synaptic drives to the motor units during the three different tasks.

Arithmetic operations in optical computations using a modified trinary number system

A modified trinary number (MTN) system is proposed in which any binary number can be expressed with the help of trinary digits (1, 0, 1 ). Arithmetic operations can be performed in parallel without the need for carry and borrow steps when binary digits are converted to the MTN system. An optical implementation of the proposed scheme that uses spatial light modulators and color-coded light signals is described.