GLUCOSE METABOLISM OF TWO STRAINS OF MYCOPLASMA LAIDLAWII

RESPIRATORY PATHWAYS IN THE MYCOPLASMA. II. PATHWAY OF ELECTRON TRANSPORT DURING OXIDATION OF REDUCED NICOTINAMIDE ADENINE DINUCLEOTIDE BY MYCOPLASMA HOMINIS

VanDemark, P. J. (University of South Dakota, Vermillion), and P. F. Smith. Respiratory pathways in the Mycoplasma. II. Pathway of electron transport during oxidation of reduced nicotinamide adenine dinucleotide by Mycoplasma hominis. J. Bacteriol. 88:122-129. 1964.-Unlike the flavin-terminated respiratory pathway of the fermentative Mycoplasma, the respiratory chain of the nonfermentative M. hominis strain 07 appears to be more complex, involving quinones and cytochromes in addition to flavins. In addition to reduction by reduced nicotine adenine dinucleotide (NADH) and reduced nicotine adenine dinucleotide phosphate, nonpyridine nucleotide-linked reduction of the respiratory chain of this organism occurred with succinate, lactate, and short-chained acyl coenzyme A derivatives as electron donors. Enzymes catalyzing the oxidation of NADH included an NADH oxidase, a diaphorase, a quinone reductase, and a cytochrome c reductase. The oxidation of NADH was sensitive to a variety of inhibitors, including 10(-4)m Atabrine, 10(-3)m sodium amytal, 10(-5)mp-chloromercuribenzoate, 10(-4)m antimycin A, and 10(-4)m potassium cyanide. The oxidase was resolved by the addition of 5% trichloroacetic acid and reactivated by the addition of flavin adenine dinucleotide but not flavin mononucleotide. The M. hominis sonic extract contained an NADH-coenzyme Q reductase. The oxidation of NADH was stimulated by the addition of either menadione or vitamin K(2) (C(35)). The oxidase was inactivated by extraction with ether or irradiation at 360 mmu. The ether-inactivated enzyme was partially reactivated by the addition of "lipid" extract of the enzyme and coenzyme Q(6). Difference spectra of the cell extracts revealed the presence of "b" and "a" type cytochromes. These cell extracts were found to contain a cyanide-and azide-sensitive cytochrome oxidase and catalase.

EVIDENCE FOR A TRICARBOXYLIC ACID CYCLE IN MYCOPLASMA HOMINIS

VanDemark, P. J. (Cornell University, Ithaca, N.Y.), and P. F. Smith. Evidence for a tricarboxylic acid cycle in Mycoplasma hominis. J. Bacteriol. 88:1602-1607. 1964.-Resting cells of acetate-grown Mycoplasma hominis strain 07 oxidized the various intermediates of the tricarboxylic and glyoxylate cycles, with the exception of sodium citrate and glyoxylate. Extracts of these cells possessed isocitric dehydrogenase, isocitratase, alpha-ketoglutaric dehydrogenase, succinic dehydrogenase, fumarase, malic dehydrogenase, citratase, and acetyl coenzyme A kinase activities. With the assay conditions employed, condensing enzyme, malate synthetase, and phosphotransacetylase activities were negligible. Incubation of sodium acetate-2-C(14) with the various intermediates of the tricarboxylic acid cycle in the presence of cell-free extracts resulted in exchange of the isotope with these compounds as well as the formation of other labeled intermediates of the tricarboxylic acid cycle. Oxidation of sodium acetate-2-C(14) alone resulted in the formation of labeled succinate, fumarate, and malate.

Purine metabolism in Acholeplasma laidlawii B: novel PPi-dependent nucleoside kinase activity

Acholeplasma laidlawii B-PG9 was examined for 16 cytoplasmic enzymes with activity for purine salvage and interconversion. Phosphoribosyltransferase activities for adenine, guanine, xanthine, and hypoxanthine were shown. Adenine, guanine, xanthine, and hypoxanthine were ribosylated to their nucleoside. Adenosine, inosine, xanthosine, and guanosine were converted to their base. No ATP-dependent phosphorylation of nucleosides to mononucleotides was found. However, PPi-dependent phosphorylation of adenosine, inosine, and guanosine to AMP, inosine monophosphate, and GMP, respectively, was detected. Nucleotidase activity for AMP, inosine monophosphate, xanthosine monophosphate, and GMP was also found. Interconversion of GMP to AMP was detected. Enzyme activities for the interconversion of AMP to GMP were not detected. Therefore, A. laidlawii B-PG9 cannot synthesize guanylates from adenylates or inosinates. De novo synthesis of purines was not detected. This study demonstrates that A. laidlawii B-PG9 has the enzyme activities for the salvage and limited interconversion of purines and, except for purine nucleoside kinase activity, is similar to Mycoplasma mycoides subsp. mycoides. This is the first report of a PPi-dependent nucleoside kinase activity in any organism.

The metabolic pathways of Acholeplasma and Mycoplasma: an overview

The metabolism of the Mollicutes Acholeplasma and Mycoplasma may be characterized as restricted, for example, by virtue of the apparent absence of cytochrome pigments. Some Mollicutes have lowered ECA values during their logarithmic growth phase, which we speculate may be related to insufficient substrate phosphorylation or insufficient ATP synthesis linked to glycolysis. We found that PEP is carboxylated by preparations of A. laidlawii, but not by other Mollicutes; thus in this organism oxaloacetate from PEP may be a link to other pathways. We found phosphoribosylpyrophosphate in A. laidlawii, which suggests that ribosylation of purines and pyrimidines occurs in Mollicutes other than M. mycoides.

Adenylate energy charge in Acholeplasma laidlawii

Adenosine 5'-triphosphate, adenosine 5'-diphosphate, and adenosine 5'-monophosphate were produced by Acholeplasma laidlawii B-PG9 growing in modified Edward medium. The adenylate energy charge was calculated to be 0.84 +/- 0.07 and ranged from 0.91 to 0.78 during exponential growth (12 to 24 h). During exponential growth, A. laidlawii contained, at 17.5 h, 2.3 X 10(-17) mol of adenosine 5'-triphosphate per colony-forming unit and, at 16 h, 27.3 nmol of adenosine 5'-triphosphate per mg (dry weight). The medium supported a doubling time of 0.95 h. The molar growth yields (Yglucose = grams [dry weight] per mole of glucose used) were 40.2 +/- 3.4 (16 h) and 57.1 +/- 9.7 (20 h) during midexponential growth. A maximum yield of 8.3 X 10(9) colony-forming units was reached at 24 h, when 56% of the initial concentration of glucose had been used. At 40 h, during the stationary phase, 14.95 +/- 3.75 mumol of glucose per ml of medium had been used. At this time, the culture fluids contained 21.86 +/0 mumol of lactate per ml and 3.14 +/- 0.13 mumol of pyruvate per ml.

On the possible role of respiratory activity of Acholeplasma laidlawii cells in sugar transport

1. Out of 20 exogeneous substrates only ethanol and, to a much lesser extent, lactate and pyruvate were shown to be capable of stimulating the respiration of Acholeplasma laidlawii cells. However, none of these substrates changed the initial rate of active transport of 3-O-methyl-D-glucose (3-O-MG). 2. From inhibitory analyses and spectroscopic data, it is apparent that the respiratory chain of A. laidlawii has no cytochromes and is probably not responsible for oxidative phosphorylation. 3. Valinomycin and nigericin stimulated cell respiration only in the presence of K+-ions, while monensin stimulated it in the presence of Na+-ions. 4. 3-O-MG transport was shown to be sensitive to uncouplers, ATPase inhibitors and arsenate are resistant to a majority of respiratory inhibitors tested. This suggested that there was no relationship between respiration and carbohydrate transport in the A. laidlawii cells. Further evidence was provided by the absence of respiratory stimulation during the transport of non-metabolizing carbohydrates.

Occurrence and properties of lactic dehydrogenases of fermentative mycoplasmas

Eight fermentative mycoplasmas differing in genome size, deoxyribonucleic acid (DNA) base composition, or sterol dependence were examined for lactic dehydrogenase composition by spectrophotometric assay and polyacrylamide gel electrophoresis. Three completely different patterns of lactic dehydrogenase composition were found. (i) A nicotinamide adenine dinucleotide (NAD)-dependent l(+)-lactic dehydrogenase was found in Mycoplasma pneumoniae, M. gallisepticum, M. mycoides var. mycoides, mycoplasma UM 30847, M. neurolyticum, and Acholeplasma axanthum. Electrophoresis of cell-free extracts of each of these mycoplasmas produced, with the exception of M. mycoides var. mycoides and UM 30847, single, different enzyme bands. M. mycoides var. mycoides and UM 30847 were similar and formed multiple bands of enzyme activity. We were unable to establish whether these multiple bands were due to lactic dehydrogenase isoenzymes or artifacts. (ii) An NAD-dependent d(-)-lactic dehydrogenase which could not be reversed to oxidize lactate was found in M. fermentans. (iii) A. laidlawii A possessed an NAD-independent d(-)-lactic dehydrogenase capable of reducing dichlorophenol-indophenol, and an NAD-dependent l(+)-lactic dehydrogenase which is specifically activated by fructose-1,6-diphosphate. Heretofore, this enzyme regulatory mechanism was known to occur only among the Lactobacillaceae. No yeast-type lactic dehydrogenase activity was found in any of the mycoplasmas examined. The stereoisomer of lactic acid accumulated during growth correlated perfectly with the type of NAD-dependent lactic dehydrogenase found in each mycoplasma. The types of lactic dehydrogenase activity found in these mycoplasmas were not related to genome size, DNA base composition, or sterol dependence.