Nonsubstrate induction of a soluble bacterial cytochrome P-450 monooxygenase by phenobarbital and its analogs

A soluble, cytochrome P-450-dependent fatty acid hydroxylase--epoxidase complex from Bacillus megaterium ATCC 14581 can be induced more than 100-fold by the addition of phenobarbital or one of its analogs (hexobarbital) to the growth medium. These barbiturate inducers are apparently not substrates for the enzyme nor do they activate the monooxygenase in the cell-free system. The induction efficiency of both phenobarbital and hexobarbital can be significantly increased with respect to monooxygenase activity by autoclaving the inducer in the growth medium rather than by adding it to the medium after autoclaving. Turnover numbers of about 3 000 nmoles of substrate oxygenated per min per nmole of P-450 were obtained in crude cell-free preparations obtained from maximally induced cultures. Our data indicate that products formed by heating phenobarbital or hexobarbital in the growth medium are significantly better inducers of monooxygenase activity than are the unaltered drugs.

Oxygen effect, hydrogen peroxide yields, and time scale of interaction of potentially damaging species in electron pulse irradiated bacterial spores

A given integrated radiation dose delivered from a LINAC as a train of pulses (50/s), characteristically of 0.1 to 5 microseconds pulse length with dose rates within the pulse between 0.38 and 38 krads/microsecond, inactivates bacterial spores in water suspension more effectively than the same dose given as Co60 gamma rays. This enhancement of radiation damage occurs both in the presence and in the absence of oxygen and is not explained by either pulse dose rate or pulse length alone, but is monotonically related to the product of these pulse parameters, pulse dose. The enhancement appears to result from the interaction, within individual spores, of free radical species of average lifetime of about 2-5 microseconds. The time scale over which these species operate suggests that they are freely diffusable. Prevention, in part, of their damaging effect by the presence of selective scavenging agents is evidence that OH radicals are involved. Measurements of H2O2 yield for irradiation conditions that show a gradation of enhancement of damage correlate strongly with the extent of damage observed.

Reversion by vitamin K of aflatoxin B1 (AFB)-induced inhibition of oxygen uptake in three AFB-susceptible bacteria

The effect of Vitamin K, on the inhibition of oxygen uptake in Bacillus brevis (2611), Bacillus megaterium (1368) and Flavobacterium aurantiacum by aflatoxin B1 (AFB) has been investigated. At 1.5 mM, vitamin K completely reversed oxygen inhibition by 10 micrograms/ml AFB in the three bacteria and by 50 micrograms/ml AFB in B. brevis, the most susceptible of the three bacteria to AFB. Vitamin K did not reverse the inhibitory effect of 100 micrograms/ml AFB in any of the three bacteria except B. megaterium, neither did 1.5 mM 2,4-dinitrophenol (DNP) reverse the inhibition at 10 micrograms/ml and 100 micrograms/ml levels of AFB in any of the three bacteria.

Responses of cells to radiation sensitizers: methods of analysis

Several well-known transforms of the widely-used Michaelis-Menten function linearize the kinetics of many competition reactions such as enzymatic processes. These transforms allow easy and accurate evaluation of the mathematical constants of the system, as well as giving clues to the various mechanisms involved in these competitions. In this paper these linearization techniques are applied to several sets of data from several authors that describe the radiation sensitivity determined by varied concentrations of two sensitizers--O2 and misonidazole. It is shown that, when the increment in sensitivity determined at the various concentrations of sensitizer is used as the dependent variable, straight lines are obtained from various sets of data when either the so-called Lineweaver-Burk or the Eadie-Hofstee transform is used. The E-H transform results in a better distribution of data points and, accordingly, is preferred. The transform allows recognition of two oxygen-dependent processes (one at low [O2] and one at high [O2]) in data apparently demonstrating but one; and, as well, two processes determined at two levels of misonidazole from data that appeared to describe one. These results support the evidence given earlier for two oxygen effects in other cells. Also, the transform reveals that in different cell systems two inhibitors of the oxygen effect appear to act in the same manner on one oxygen effect and in a different way on the other. In discussion the value of the transform in analysing mechanisms of sensitization is examined, and its further potential use in understanding the action of chemical protective agents is pointed out.

Synthesis of the antibacterial peptide cecropin A (1-33)

Cecropin A(1-33) was synthesized by an improved stepwise solid-phase method. The synthesis was designed to give high coupling yields and minimal amounts of byproducts. All coupling steps were monitored for completion by a new ninhydrin procedure, and the fully protected peptide-resin was analyzed for deletion peptides by the solid-phase Edman preview technique. Both methods indicated that the average coupling yield was greater than 99.8%. The unpurified peptide mixture resulting from HF cleavage and extraction into 10% acetic acid was analyzed by reverse-phase high-pressure liquid chromatography, and 93% of the total product was shown to be the desired [Trp(For)2]cecropin A(1-33), indicating an average yield per synthetic cycle of 99.8%. Removal of the formyl group at pH 9, followed by ion-exchange chromatography, gave the purified product. Cecropin A(1-33) showed antibacterial activity against both Gram-positive and Gram-negative bacteria. Against Escherichia coli, the activity was only slightly lower than that of the natural 37-residue cecropin A when tested over a 100-fold concentration range; the minimum inhibitory concentration was approximately 1 microM. The formyl derivative was somewhat less effective in killing E. coli than the free 1-33 peptide. The antibacterial activity was discussed in terms of an amphipathic alpha-helix structure and the binding of the peptide to bacterial membranes.

Interaction of beta-lactam antibiotics with penicillin-binding proteins from Bacillus megaterium

The binding properties of 25 beta-lactam antibiotics to Bacillus megaterium membranes have been studied. The affinities of the antibiotics for the penicillin-binding proteins (PBPs) are also reported. We found that PBP 4 has the highest affinity for nearly all the antibiotics studied whereas PBP 5 has the lowest affinity. Both PBP 4 and PBP 5 appear to be dispensable for the maintenance of bacterial growth and survival and appear to be DD-carboxypeptidases. Only the beta-lactam cefmetazol bound preferentially to PBP 5 and has been used to study the inhibition of DD-carboxypeptidase. Comparative studies with beta-lactam that simultaneously result in (a) binding to PBPs 1 and 3, (b) inhibition of cell growth and (c) lysis, stressed the importance of PBPs 1 and 3 for cell growth and survival.

Phenobarbital induction of a soluble cytochrome P-450-dependent fatty acid monooxygenase in Bacillus megaterium

A soluble, cytochrome P-450-dependent fatty acid hydroxylase-epoxidase isolated from Bacillus megaterium ATCC 14581 can be induced about 28-fold by the addition of phenobarbital (8 mM) to the growth medium. Phenobarbital is not a substrate for the enzyme nor does it activate the monooxygenase in the cell-free system. The level of the P-450-dependent monooxygenase activity in cultures harvested during the early stationary phase of growth increased linearly with phenobarbital concentration up to its solubility limit (8 mM) at 35 degrees C. The time course of induction during culture growth in the presence of 4 mM phenobarbital showed an interesting dichotomy. The specific content of cytochrome P-450 increased until the early stationary phase of growth and then leveled off. P-450-dependent monooxygenase activity, however, continued to increase rapidly to midstationary phase and then decreased just as rapidly after this time. At maximum specific activity, a turnover number of about 2,450 was obtained for palmitoleate hydroxylation-epoxidation by the cytochrome P-450 system.

Commitment of bacterial spores to germinate. A measure of the trigger reaction

The rate of commitment of bacterial spores to germinate after short exposure to L-alanine increases exponentially from the time of addition of L-alanine. This absence of a lag facilitates kinetic analysis and allows the dependence of commitment on temperature and pH to be determined. The pH profile of commitment has been compared with that obtained from measurements of absorbance decreases during germination, and the two profiles exhibit differing pK values. It is suggested that because the decrease in A600 of spore suspensions is a late event in germination, it is an unsuitable parameter for studying germination-triggering reactions. Commitment has been shown to be temperature-dependent, with an optimum at approx. 37 degrees C and an activation energy (mu) of 1.08 X 10(5) J/mol. The data obtained from the present studies have been used to develop a model for the triggering of germination.

[Effect of polyene antibiotics on bacterial protoplasts]

The carbonyl-conjugated pentaenes flavofungin, nigrofungin and flavopentin exhibit considerable lytic activity toward Micrococcus lysodeikticus and Bacillus megaterium protoplasts. The antibiotics at concentrations of 5 to 14 microgram/ml cause lysis of 50% of the protoplasts within 15 min of their incubation. The antibiotics inhibit the activity of NADH oxidase and malate oxidase by 50% in the lysates of Micrococcus lysodeikticus and Bacillus megaterium protoplasts at concentrations of 30 to 50 microgram/ml; preincubation of the lysates with the antibiotics intensify the inhibiting action of the polyenes. Growth of the bacteria is inhibited when the minimal concentration of the polyenes is 75 to 100 microgram/ml. Interaction of the polyenes with bacterial membranes lacking sterols indicates that resistance of at least some bacteria to polyenes is caused by impermeability of the cell wall for these substances rather than by the absence of sterols in the membranes.

[Effect of the protein synthesis inhibitor chloramphenicol on the basic growth indices of continuous and periodic Bacillus megaterium cultures]

The action of chloramphenicol, a specific inhibitor of bacterial growth and an inhibitor of protein synthesis, was studied in the conditions of continuous and batch cultivation. Steady states of the population within the range of D from 0.2 to 0.7 hr-1 were obtained at a concentration of the antibiotic equal to 20 microgram per liter. The shape of the chemostat curve in the presence of chloramphenicol in the medium indicates that the antibiotic slightly decreases mu max and considerably diminished Y. A change of limiting factors occurs along the chemostat curve at different dilution rates (0.2, 0.4 and 0.7 hr-1): one-, two- and three-factor effects on the population were observed. Steady states of the population in the chemostat are possible by chloramphenicol concentrations of 10 to 100 microgram per litre; in this case, cellular metabolism changes in the following nonspecific way: less effective energy processes are activated, the Y decreases as well as protein content in the cells, but the content of poly-beta-hydroxybutyric acid in the biomass increases. If chloramphenicol is taken at a concentration of 1000 microgram per litre (a dose strongly inhibiting the growth rate), other changes specific for this inhibitor are found: the content of protein decreases while that of RNA increases, and substances of nucleotide nature are released into the medium. The changes remain for many generations. The data show that it is possible to change the ratio between cell polymers in growing population.

Peptidoglycan turnover during growth recovery after chloramphenicol treatment in a Dap-Lys-mutant of Bacillus megaterium

The study of diaminopimelic acid (DAP) incorporation and turnover during growth recovery in chloramphenicol-treated (CMP-treated) Bacillus megaterium cells showed that two kinds of turnover occurred. A low acid-soluble turnover appeared as soon as growth resumed in bacteria labeled before the CMP treatment and at the middle of the first generation in those labeled during the treatment. The acid-insoluble turnover appeared only at the beginning of the second generation of growth resumption in bacteria labeled before CMP addition and at the beginning of the third generation in those labeled during the CMP treatment. The acid-soluble release observed during the period of cell wall thinning is too low to account for the decrease of the wall thickness and the acid-insoluble loss appears after this period. When bacteria were transferred into partially spent medium instead of fresh culture medium the acid-insoluble release started to appear half a generation sooner. Electron microscopic observations showed that in this case, large scales detached from the cell wall. This activity of wall degradation was not observed when the partially spent medium was previously heated for 10 min at 100 degree C. The persistence of a thick wall on cell ends during the first generation does not reflect an absence of growth sites because their labeling on autoradiographs is high. Rather, it seems to be due to a low lytic activity at the poles.

Regulation of phosphoglycerate phosphomutase in developing forespores and dormant and germinated spores of Bacillus megaterium by the level of free manganous ions

The large depot of phosphoglyceric acid (PGA) which is accumulated within spores of Bacillus megaterium is greater than 99% 3-phosphoglyceric acid (3-PGA). The 3-PGA depot is stable in forespores and dormant spores, but is utilized rapidly during spore germination. When spores were germinated in KBr plus NaF, the PGA depot was not utilized, but 13% of the 3-PGA was converted to 2-PGA. These data suggest phosphoglycerate phosphomutase as the enzyme which is regulated to allow 3-PGA accumulation during sporulation. Young isolated forespores, in which 3-PGA was normally stable, utilized their 3-PGA rapidly when incubated with Mn2+ plus the divalent cation ionophore X-537A; Mn2+ or ionophore alone or Mg2+ or Ca2+ plus ionophore was without effect. Young forespores contained significant amounts of Mn2+. However, forespore Mn2+ exchanged slowly with exogenous Mn2+ and was removed poorly by toluene treatment. This suggests that much of the forespore Mn2+ is tightly bound to some forespore component. Since phosphoglycerate phosphomutase from B. megaterium has an absolute and specific requirement for Mn2+, these data suggest that the activity of this enzyme in vivo may be regulated to a large degree by the level of free Mn2+. Indeed, the activity of this enzyme in forespore or dormant spore extracts was stimulated greater than 25-fold by Mn2+, whereas comparable extracts from cells or germinated spores were stimulated only two- to fourfold.