Fortimicins A and B, new aminoglycoside antibiotics. I. Producing organism, fermentation and biological properties of fortimicins

A culture of Micromonospora species MK-70 was found to produce two new antibiotics, fortimicins A and B. Antibacterial and paper chromatographic data on an eluate from IRC-50 treatment of fermentation beers indicated that fortimicins A and B are new antibiotics with broad-spectrum, basic and water-soluble properties. Fortimicin A exhibited potent, unique, broad-spectrum antibacterial activity against Gram-positive and negative bacteria both in vitro and in vivo, while fortimicin B was only weakly active.

Mechanism of thyroxine-mediated oxidation of reduced nicotinamide adenine dinucleotide in peroxidase-H2O2 system

The oxidation of reduced nicotinamide adenine dinucleotide (NADH) by the horseradish peroxidase (HRP)-H2O2 system is greatly increased by the addition of thyroxine or related compounds. On the basis of a study of the rate of NADH oxidation in the presence of various concentrations of thyroxine, it is clear that thyroxine acts as a catalyst for NADH oxidation. Spectral changes of a HRP-H2O2 complex (compound I) indicate that thyroxine acts as an electron donor to both compounds I and II. The rate of electron donation from thyroxine is much faster than that from NADH. The HRP-H2O2 system requires 0.83 mol of O2 for the oxidation of 1 mol of NADH. Ferricytochrome c is reduced to ferrocytochrome c by the system, and causes an inhibition of O2 consumption which can be abolished by superoxide dismutase. JUDGING FROM THE INHIBITION OF O2 uptake by ferricytochrome c, about 54% of the total flux of electrons from NADH to oxygen appears to proceed by way of O2-. These results suggest that the initial step of thyroxine-mediated NADH oxidation by HRP and H2O2 is the formation of oxidized thyroxine, a phenoxy radical, which attacks NADH to produce NAD.

Metabolic role of free mycolic acids in Mycobacterium tuberculosis

Small amounts of free mycolic acids and trehalose dimycolate that are rapidly formed by Mycobacterium tuberculosis H37Ra are probably derived from mycolyl acetyl trehalose and transferred to the cell wall. However, the transfer of mycolic acids from mycolyl acetyl trehalose to the cell wall still appears to be the more prominent route.

Enzymatic synthesis of 2-O-alpha-D-mannopyranosyl-methyl-alpha-D-mannopyranoside by a cell-free particulate system of Mycobacterium smegmatis

A cell-free particulate enzyme preparation of Mycobacterium smegmatis ATCC 607 catalyzed the transfer of labeled mannose from GDP[14C] mannose to methyl-alpha-D-mannopyranoside (an exogenously added acceptor) to form a product that was characterized to be 2-O-alpha-D[14C] mannopyranosyl-methyl-alpha-D-mannopyranoside. This transmannosylase activity was specific for both the sugar nucleotide donor and methyl monosaccharide acceptor. The reaction was stimulated by the addition of various metal ions and had a pH optimum of 6.0. The apparent Km of this transmannosylase reaction for methyl-alpha-D-mannopyranoside was 35 mM. The possible relationship between this "artificial" mannosyl-transfer system and the "natural" system which leads to the formation of the oligomannosides and glycoproteins is discussed.

Isolation, characterization, and function of 6-mycolyl-6'-acetyltrehalose in the H37Ra strain of Myocobacterium tuberculosis

The major mycolic acid containing extractable lipid of the H37Ra strain of Mycobacterium tuberculosis was established to be 6-mycolyl-6'-acetyltrehalose (MAT). This new glycolipid was extracted from harvested cells with chloroform-methanol (2:1, v/v) and initially precipitated out in acetone. A series of column (DEAE-cellulose, silicic acid, and Sephadex LH-20) and preparative thin-layer chromatography steps yielded a homogeneous preparation. A single sugar was released by saponification and it was identified to be trehalose by paper chromatography and gas-liquid chromatography of the trimethylsilyl derivative. The lipid moiety was determined to be exclusively mycolic acids. The major mycolic acid component of this glycolipid was isolated, purified as the methyl ester, and characterized to be methyl alpha-mycolate by nuclear magnetic resonance spectroscopy and mass spectrometry. The molar ratio of trehalose to mycolic acids was determined to be 1:1. The other acyl group in MAT was established to be acetate by gas-liquid chromatography. Methylation analysis showed the mycolate and acetate ester linkages to the 6 and 6' positions of trehalose. The time course of incorporation of 14C-labeled acetate into the mycolates of both MAT and total cellular fatty acids was followed. These results showed that the synthesis of MAT is rapid and linear for the initial 20 min of incubation whereas the curve for the total cellular mycolates minus MAT (an estimate of the cell wall mycolates) had a 25-30-min lag period. When the label in the lipids was chased out with an excess of unlabeled acetate, relatively rapid decline in the labeled MAT resulted with a corresponding rise in the level of radioactivity in the mycolates of the nonextractable cellular fraction (assumed to be the cell wall fraction). Thus mycolic acids are rapidly transferred from MAT to the cell wall of M. tuberculosis.

Site of inhibitory action of isoniazid in the synthesis of mycolic acids in Mycobacterium tuberculosis

The cellular mycolate synthetase activity of Mycobacterium tuberculosis H37Ra was previously shown to be very sensitive to isoniazid (Wang, L., and K. Takayama. 1972. Antimicrob. Agents Chemother. 2: 438-441). We have now examined the question of how isoniazid inhibits the synthesis of mycolic acids. The saponifiable 14-C-labeled lipids of control and isoniazid-treated cells (1.0 mug/ml, 60 min) were compared on a Sephadex LH-20 column, and it appeared that the synthesis of the intermediate-sized fatty acids was partially inhibited. These fatty acids were fractionated as their methyl esters by Sephadex LH-20 column chromatograp-y and gas-liquid (6% Dexsil) chromatography. Mass sectral analysis of the fractionated lipids revealed several series of fatty acids: fraction II, C39-C56; fraction III, C27-C40. The long-chain fatty acids in three kinds of isoniazid-treated cells were examined: (a) long-term exposure (48 hr, 0.5 mug/ml), (b) short-term exposure (60 min, 1.0 mug/ml), and (c) variable exposure at low concentration (0-90 min, 0.2 mug/ml). Both long- and short-term exposure experiments showed that isoniazid inhibited the synthesis of saturated fatty acids greater than C26 and of unsaturated fatty acids greater than C24. The variable-exposure experiment at low isoniazid concentration showed that the syntheses of mycolic acids and long-chain fatty acid fractions II and III were inhibited to the same extent. These fatty acids may thus be precursors of mycolic acids.

The role of mannosylphosphorylpolyisoprenol in glycoprotein biosynthesis in Mycobacterium smegmatis

A particulate enzyme preparation of Mycobacterium smegmatis catalyzes the transfer of labeled mannose from GDP-[14C] mannose into several endogenous acceptors. In one of these transfer reactions, the radioactivity is incorporated into an insoluble polymeric product that is present at the interphase after extraction of reaction mixture with chloroform-methanol. Solubilization of this product was achieved by digestion with proteolytic enzymes or treatment with 0.1 M NaOH indicating that the material was glycoprotein in nature. The solubilized material obtained after proteolytic digestion followed by treatment with alkali (representing 80-93% of the total interphase product) was shown to consist of a series of small molecular weight [14C] mannose containing oligosaccharides and glycopeptides by Bio-Gel column chromatography. A kinetic study of the enzymatic transfer of [14C] mannose from GDP-[14C] mannose into the glycoprotein suggested that the mannosylphosphorylpolyisoprenols are the obligatory mannosyl donor.