Functional characterization of constituent enzyme fractions of mycobacillin synthetase

The enzyme fraction A, a constituent enzyme of the three-fraction enzyme mycobacillin synthetase, independently and sequentially activated five amino acids starting from L-proline, producing the pentapeptide Pro(Asp1,Glu1,Tyr1)Asp. The fractions B and C were unable to function independently. However, the fraction B synthesized the nonapeptide Pro(Asp3,Glu1,Tyr2,Ser1)Leu, sequentially activating the pentapeptide and next four amino acids, whereas the fraction C synthesized mycobacillin by the sequential activation of the nonapeptide and the remaining four amino acids. The pH optima of the above enzymes are almost identical (pH 7.8), but their Km values are a little different.

Sensitized photo-oxidation of bovine alpha-crystallin: change in microenvironments of thiol groups

Methylene blue- or riboflavin-sensitized photo-oxidation of alpha-crystallin caused a major change in the environment of thiol groups of the protein which could not be significantly prevented by inhibitors specific for active species of oxygen, 1O2, .OH, O.2, and H2O2. In contrast, the sensitizer N-formylkynurenine had no such effect. Sensitizer-induced change in the microenvironments of thiol groups was attributed to a conformational alteration, probably an unfolding of the protein.

Age-related changes in protein conformation in bovine lens crystallins

In order to investigate the conformational changes associated with the aging process, circular dichroism (CD), absorption and fluorescence measurements of bovine lens crystallins isolated from the nucleus of old (cow) and young (calf) animals are reported. Results show considerable differences in spectroscopic parameters between the young and old alpha-crystallin; however, no such changes were observed for beta- and gamma-crystallins. Age-related changes include an increased absorption in near-u.v. and decreased intensity in the far-u.v. region; near-u.v. circular dichroism shows a considerable difference, whereas the dichroism in far-u.v. remains the same. The decrease in tryptophan fluorescence of old alpha-crystallin is of the same magnitude as is the increase in non-tryptophan fluorescence. The fluorescence of the sulfhydryl (SH) specific probe, 2-(4'-maleimidylanilino) naphthalene-6-sulfonate, indicates that accessible (to the probe) SH groups of cow alpha-crystallin are fewer than those of calf, and they are also in a more polar environment. This study demonstrates that, with aging, alpha-crystallin undergoes a change in the tertiary structure involving tryptophan, tyrosine and cysteine residues. This conformational change has been explained by the suggestion that a large portion of the protein unfolds during the aging process, resulting in a change in interaction properties between the aromatic amino acid residues and between the residues and the peptide backbone. The unfolding is also associated with the accessibility, reactivity and spatial arrangement of these residues, including the cysteine by which aggregation or cross-linking of the protein is likely to occur.

Translocation of mycobacillin synthetase in Bacillus subtilis

The extracellular release of mycobacillin from Bacillus subtilis first occurred in the medium at the onset of stationary phase and continued at a high rate even after 6 days. Mycobacillin synthetase activity appeared earlier than late-exponential phase in the cytosol of producer cells and was not sedimentable even at 105 000 g. The activity then quickly reached the maximum late in the stationary phase. With further increase in the age of the culture, the activity gradually disappeared from the cytosol, to reappear concomitantly in the membrane in an insoluble particulate form, even in absence of protein synthesis. The membrane-bound synthetase activity was sedimentable at 10 000 g and was fairly active even after 5 days.

Accumulation of peptides by mycobacillin-negative mutants of Bacillus subtilis B3

Thirteen mycobacillin-negative (My-) mutants of Bacillus subtilis B3 were isolated from an auxotrophically tagged mycobacillin producer organism. The wild-type producer, three feeble producers and three strictly My- mutants did not accumulate any ninhydrin-positive peptide in the culture medium while the remaining seven My- mutants did accumulate ten such peptides whose amino acid composition indicated that there might be only three different peptides. The N-terminal and C-terminal amino acid residues implicated one of these peptides as a pentapeptide intermediate in mycobacillin synthesis; this was further confirmed by its molecular weight and sequence. Studies on cell-free synthesis showed that only the enzyme system from the wild-type strain synthesized mycobacillin while the defective ones from all the My- mutants synthesized one and the same pentapeptide as found in the culture broth of some of the mutants. Further studies in which the enzymes responsible for mycobacillin synthesis by cell-free extracts were separated into three fractions, A, B and C, showed that seven of the mutants were defective in fraction B whereas the three other mutants had defects in both fractions B and C. Thus the pentapeptide Pro----Asp----Glu----Tyr----Asp appears to be implicated in mycobacillin biosynthesis.

Mycoversilin, a new antifungal antibiotic. III. Mechanism of action on a filamentous fungus Trichophyton rubrum

Mycoversilin is active against filamentous fungi, being specifically inhibitory to Trichophyton rubrum, minimum inhibitory concentration being 15 micrograms/ml. Mycoversilin inhibits sporulation to the extent of 28.5% even at the growth inhibitory concentration whereas inhibition of spore germination requires higher concentration. It has no effect on radial growth. Further it shows no action either on the release of UV absorbing materials or on the respiration of T. rubrum. However, the antibiotic inhibits in vivo synthesis of protein fairly strongly, DNA moderately and RNA slightly at the minimum inhibitory concentration. Cell-free protein synthesis is also strongly inhibited, the site of action being the inhibition of leucyl-tRNA formation by the antibiotic which has no action on leucine activation.

Standardization of parameters for the mycobacillin synthetase activity

An effective method of preparation involving sonication was developed for cell-free mycobacillin synthetase from Bacillus subtilis. The enzyme showed optimum activity at a buffer concentration of 50 mM (Tris-HCl) and pH 7.5. ATP and Mg2+ which were essential for synthesis showed an optimum requirement at a ratio of 1:1. The synthetase was markedly inhibited by ADP whereas AMP was without any effect. ATP or ATP-generating system could not be replaced by GTP, UTP or CTP. Co2+ and Mn2+ could to some extent substitute Mg2+. Mercapto reagents inhibited the antibiotic synthesis. Exogenous addition of pantothenic acid had no effect.

Mycoversilin, a new antifungal antibiotic. II. Structure elucidation

The structure of a new antifungal antibiotic, mycoversilin, produced by Aspergillus versicolor (N5)17 was determined as I by various spectroscopic and chemical methods. Mycoversilin is a unique polynuclear aromatic compound having two methyl and six hydroxyl groups and two ether linkages. The acetyl derivative prepared was found to have no antifungal property.

Mycoversilin, a new antifungal antibiotic. I. Fermentation, isolation and biological properties

A new antifungal antibiotic, mycoversilin, was isolated from the culture filtrate of Aspergillus versicolor (N5)17 by repeated column chromatography and recrystallized from ethyl acetate as homogeneous fine needles. Maximum production took place in a medium containing 4% glucose and 1% peptone at pH 3.5, temperature 28 degrees C after 8-9 days of incubation under stationary condition. Mycoversilin is a narrow spectrum antibiotic with activity against filamentous fungi, particularly Trichophyton rubrum (MIC 15 micrograms/ml).

Fractionation of the mycobacillin-synthesizing enzyme system

The mycobacillin-synthesizing enzyme system was highly purified by fractionation at 30-55% (NH4)2SO4 saturation. The enzyme concentrate on Sephadex G-200 gel chromatography was resolved into three distinct fragments. Each of the fragments on further purification by DEAE-cellulose ion-exchange chromatography behaved as a single-component system, as clearly indicated by the sharpness of the peaks in the elution diagram. None of the fragments alone nor any two of them in all possible combinations possessed mycobacillin-synthesizing activity, which was restored only when the three fragments were used together in the test system.

Influence of lectins, hexoses, and neuraminidase on the association of purified elementary bodies of Chlamydia trachomatis UW-31 with HeLa cells

Using highly purified elementary bodies of Chlamydia trachomatis UW-31 (serotype K), we found that HeLa 229 monolayer cultures bound more 32P-labeled chlamydiae after pretreatment with the lectin wheat germ agglutinin. The lectin, on the other hand, inhibited competitively when chlamydial association was assayed in the presence of polycations. The two effects of wheat germ agglutinin were abolished when N-acetylneuraminic acid (NeuNAc)- or N-acetylglucosamine (GlcNAc)-preincubated wheat germ agglutinin was used. Brief exposure of HeLa cells to neuraminidase abolished the ability to bind the elementary bodies, whether or not polycations were present. Furthermore, at 5 degrees C but not at 37 degrees C, NeuNAc, GlcNAc and N-acetylgalactosamine inhibited chlamydial association only in the absence of the polycation DEAE-dextran. The results suggest that NeuNAc residues on the plasma membrane are the principal, but not the only, receptors for this strain of C. trachomatis.

Purification of Chlamydia trachomatis lymphogranuloma venereum elementary bodies and their interaction with HeLa cells

A procedure has been developed to yield infectious elementary bodies of the lymphogranuloma venereum strains LGV 434 and 404 of Chlamydia trachomatis, labelled during intracellular growth in HeLa 229 cells. The final preparation, obtained after velocity sedimentation of a polycarbonate membrane-filtered sample through a sucrose gradient, is free of host proteins and, more importantly, of chlamydial reticulate bodies. Using such purified preparations, it was found that the association of LGV 434 elementary bodies with HeLa 229 cultures was unaffected by the pretreatment of the host cells with a variety of lectins or with neuraminidases from Clostridium perfringens and Vibrio cholerae. The association was inhibited by dextran sulphate and by mild trypsin treatment of HeLa cultures. Treatment of purified elementary bodies with trypsin, chymotrypsin, neuraminidases and a variety of carbohydrates and lectins did not produce any change in the rate of association with HeLa cultures. Heat-inactivated elementary bodies were significantly less able to associate with the host cells.

Modulation of bacterial association to HeLa cell cultures by cell density and by chlamydial infection

The effect of cell density on the rate of association of Escherichia coli and Staphylococcus aureus by monolayer cultures of HeLa 229 cells was investigated. Radioactively labeled bacteria were incubated with sparsely and densely plated cells. The rate of bacterial uptake was 10- to 20-fold higher in sparse cultures. Kinetic analysis of data with different multiplicities of input bacteria showed that the Km of the reaction was unaltered, whereas the Vmax was inversely related to cell density. Pretreatment of HeLa cultures with dibutyryl adenosine 3',5'-phosphate had little effect on the rate of bacterial association. The simultaneous presence of an obligately parasitic bacterium, Chlamydia trachomatis LGV434, enhanced the Vmax of association of E. coli and S. aureus. This effect was more pronounced in dense HeLa cell cultures. Heat-inactivated chlamydiae were unable to modify the association. Enhanced association persisted for at least 3 h after infection with chlamydiae.

Exoprotease production by sporogenous and asporogenous mycobacillin non-producer mutants of Bacillus subtilis

Mycobacillin non-producers, whether sporogenous or asporogenous, possess less exoprotease, but effective exoprotease producers are not always good mycobacillin yielders. There might exist a minimum level of exoprotease formation for elaboration of mycobacillin.

Glycolytic enzyme activities in malignant cells grown in vitro and in vivo

Cell proximity has a profound effect on the glycolytic enzyme levels observed in mammalian cells grown in vitro. Hexokinase activity generally increased with the increasing cell density of both untransformed and virus-transformed cultures. In contrast, phosphofructokinase and pyruvate kinase activities were generally elevated only in crowded cultures of transformed cells. A spontaneous experimental mouse tumor cell line (EMT6) exhibited cell crowding-dependent elevations in glycolytic enzyme levels when cultured in vitro. The glycolytic enzyme levels of experimental mouse tumors grown in vivo, on the other hand, were constant and normally less than those observed in cultured EMT6 cells.