Minimum inhibitory concentration of drugs againstMycobacterium leprae as determined by anin vitro assay

The observations that liveMycobacterium leprae after entry into cultured peritoneal macrophages from mice, reduced the EA rosetting macrophages, have been exploited to determine the minimum inhibitory concentration of diamino diphenyl sulphone and rifampicin. Diamino diphenyl sulphone showed a minimum inhibitory concentration of 0.028 μg/ml and rifampicin 0.11μg/ml when given externally. However, there was accumulation of diamino diphenyl sulphone inside the macrophages. At an external concentration of 0.028 μg/ml the concentration inside the macrophage was 0.5μg/ml. The minimum inhibitory concentration for diamino diphenyl sulphone in this assay system is higher by several folds and that for rifampicin is slightly lower, than what is reported earlier with mice foot pad experiments. The minimum inhibitory concentration reported in this assay system is quite close to what is observed forin vitro inhibition ofMycobacterium lufu with both the drugs     

Clathrin-associated proteins contain bound nucleotide

An alcohol dehydrogenase isolated from Zymomonas mobilis was found to be activated by ferrous ions but not by zinc, after inactivation with metal-complexing agents. Cobaltous ions also re-activated to a lesser extent. It is suggested that in this species the alcohol dehydrogenase naturally contains iron. Kinetic studies on the iron-treated enzyme indicate an 'alcohol activation' phenomenon, which may have physiological relevance in overcoming product inhibition during fermentation.     

Isolation of the sodium-dependent d-glucose transport protein from brush-border membranes

Rabbit kidney brush-border membrane vesicles were exposed to bacterial protease which cleaves off a large number of externally oriented proteins. Na⁺-dependent d-glucose transport is left intact in the protease-treated vesicles. The protease-treated membrane was solubilized with deoxycholate and the deoxycholate-extracted proteins were further resolved by passage through Con A-Sepharose columns. Sodium-dependent d-glucose activity was found to reside in a fraction containing a single protein band of M_r ? 165000 which is apparently a dimer of M_r ? 85 000. When reconstituted and tested for transport, this protein showed Na⁺-dependent, stereo-specific and phlorizin-inhibitable glucose transport. Transport activity is completely recovered and is 20-fold increased in specific activity. A similar isolate was obtained from rabbit small intestinal brush-border membranes and kidneys from several other species of animals.     

Thyroid Hormones and Derivatives Inhibit Flunitrazepam Binding

Thyroid hormones and their derivatives were found to inhibit [3H]flunitrazepam binding stereospecifically and in a monophasic manner. Among the compounds tested, D-thyroxine was the most potent inhibitor (IC50 = 0.5 microM). The naturally occurring L-thyroxine was about 40-fold less potent (IC50 = 20 microM). The structure-activity relationships seem to imply that the thyronine base has the principal role in the inhibition of benzodiazepine receptor binding. The type of inhibition was examined with the most potent inhibitor, D-thyroxine, by Scatchard analysis. The apparent dissociation constant (KD) of the [3H]flunitrazepam binding increased and the receptor density (Bmax) decreased as a function of D-thyroxine concentration; this is characteristic of mixed-type inhibition.     

Feedback inhibition of homoserine kinase from radish leaves

Homoserine kinase is a potential control point in the biosynthetic pathway for threonine, isoleucine and methionine. The radish leaf enzyme was tested     

Interrelationships between Ethylene Production,Gall Formation,and Root-knot Nematode Development in Tomato Plants Infected with Meloidogyne javanica

Ethylene production was determined in excised tomato (Lycopersicon esculentum) root cultures of Meloidogyne javanica susceptible and resistant cultivars infected with M. javanica. Uninfected cultivars produced very low amounts of ethylene. Relatively high amounts of ethylene were produced by the infected susceptible cultivars. Peak production of 1.6 n moles * g root⁻¹ * h¹⁻ occurred between 9 and 16 days after inoculation (DAI). The period of high ethylene production coincided with that of rapid increase in gall weight. Low amounts of ethylene were also released by the infected resistant cultivar between 9 and 12 DAI, which follows the hypersensitivity reaction. Ethylene production in infected intact plants during the period of rapid gall growth was twice as much as in uninfected plants during the same time. Exposing excised root cultures to 0.5 or l0 ppm ethylene accelerated the rate of increase in gall weight of M. javanica infected roots. In contrast, overall root growth was inhibited by these treatments, compared to infected roots which were not exposed to ethylene.     

Requirements for antiribosomal activity of pokeweed antiviral protein

It has been known for some time that pokeweed antiviral protein acts by enzymatically inhibiting protein synthesis on eucaryotic ribosome systems. The site of this action is known to be the ribosome itself. In this paper we show that the pokeweed antiviral protein reaction against ribosomes is a strong function of salt concentrations, where 160 mM K⁺ and 3 mM Mg²⁺ retards the reaction, while 20 mM K⁺ and 2 mM Mg²⁺ allows maximum reaction rate. It is also shown, however, that an unidentified protein in the postribosomal supernatant solution, together with ATP, allows the ribosome to be attacked even in the presence of high salt. Kinetic analysis of the antiviral protein reaction has been carried out under both sets of conditions, and reveals that the turnover number for the enzyme is about 300–400 mol/mol per min. in each case. The K_m for ribosomes is 1 μM in the presence of low salt and 0.2 μM at higher salt in the presence of postribosomal supernatant factors plus ATP. The antiviral protein reaction is also shown to be pH dependent and is controlled by a residue with pK_a value of approx. 7.0, apparently a histidine. Stoichiometric reaction of the enzyme with iodoacetamide results in a significant loss of antiribosomal activity.     

Effect of calcium on synthesis of dipicolinic acid inPenicillium citreoviride and its feedback resistant mutant

Dipicolinic acid synthesis inPenicillium citreoviride strain 3114 was inhibited by Ca²⁺ ions, but not by Ba²⁺, Cu²⁺or Fe²⁺. Among the metals tested, only Zn²⁺ inhibited the synthesis of dipicolinic acid and promoted sporulation. None of these metals reversed the inhibition by Ca²⁺ or Zn²⁺. A mutant 27133-dpa-ca selected for resistance to feedback inhibition by dipicolinic acid: Ca²⁺ complex showed cross-resistance to inhibition by dipicolinic acid: Zn²⁺. Both 3114 and271 33-dpa-ca excreted a number of aliphatic and amino acids during secondary metabolism of dipicolinic acid. In the presence of 1000 ppm of Ca²⁺, accumulation of citric acid and α-aminoadipic acid was completely inhibited under conditions of inhibition of dipicolinic acid in parent strain 3114 but not in the mutant. Citric acid with or without Ca²⁺ did not inhibit thede novo synthesis of dipicolinic acid in the strain 3114. In fact, citric acid in the presence of Ca²⁺ improved significantly rate of dipicolinic acid synthesis. Apart from resistance to feed back inhibition by dipicolinic acid: Ca²⁺ complex, mutant differed from the parent in three other aspectsviz. (i) dipicolinic acid synthesis was not subject to catabolite repression by glucose, (ii) sporulation as well as dipicolinic acid synthesis was dependent on the presence of Ca²⁺ ions in the medium and (iii) Mg²⁺ requirement for the mutant increased three fold. Higher requirement of the Mg²⁺ could be partially relieved by Ca²⁺ during secondary metabolism. The results support the inference thatde novo synthesis of dipicolinic acid is regulated through feedback inhibition by dipicolinic acid: Ca²⁺complex.     

The influence of creosote compounds on the aerobic degradation of toluene

The inhibiting effect of 14 typical creosote compounds on the aerobic degradation of toluene was studied in batch experiments. Four NSO-compounds (pyrrole, 1-methylpyrrole, thiophene, and benzofuran) strongly inhibited the degradation of toluene. When the NSO-compounds were present together with toluene, little or no degradation of toluene was observed during 16 days of incubation, compared with a total removal of toluene within 4 days when the four compounds were absent. Indole (an N-compound) and three phenolic compounds (phenol, o-cresol, and 2,4-dimethylphenol) also inhibited the degradation of toluene, though the effect was much weaker that of the four NSO-compounds. O-xylene, p-xylene, naphthalene and 1-methylnaphthalene seemed to stimulate the degradation even though the influence was very weak. No effects of benzothiophene (an S-compound) and quinoline (an N-compound) were observed. Benzofuran (an O-compound) was identified as the compound that most inhibited the degradation of toluene. An effect could be detected even at low concentrations (40 g/l).Abbreviations bf benzofuran - bt benzothiophene - dmp 2,4-dimethylphenol - GC gas chromatograph - ind indole - mnap 1-methylnaphthalene - MAH monoaromatic hydrocarbons - mpyr 1-methylpyrrole - nap naphthalene - o-cre o-cresol - o-xyl o-xylene - phe phenol - pyr pyrrole - p-xyl p-xylene - tol toluene - thi thiophene - qui quinoline