Solubility and diffusion coefficient of adenosine 3':5'-monophosphate.

Several previously unavailable parameters of adenosine 3':5'-monophosphate have been determined. The molar extinction coefficient at pH 7.0 is 1.38 X 10(-4), the aqueous solubility at pH 7.0 is 0.0236 M and the diffusion coefficient is 4.44 X 10(-6) cm2/s.     

Metabolic regulation during early frog development. Identification of proteins labeled by 32P-glycolytic intermediates

When 32P-labeled phosphoenolpyruvate is injected into Xenopus laevis oocytes, a 50-60-kDa protein of subunit size Mr 29,000 is rapidly labeled, followed by a second (monomeric) protein of 66 kDa concomitant with the loss of label from the first protein. We have identified these proteins as, respectively, the glycolytic enzymes phosphoglyceromutase and phosphoglucomutase. The phosphoglyceromutase is labeled at a histidine and the phosphoglucomutase at a serine, presumably at their active sites during the gluconeogenic transformation of phosphoenolpyruvate into glycogen. The transfer of the 32P label from phosphoenolpyruvate to these two enzymes also occurs in in vitro lysates made from full-grown Xenopus oocytes, eggs, or early embryos, but with a slower time course. Lysates prepared from leg muscle show labeling of the phosphoglyceromutase, but not the phosphoglucomutase, when incubated with [32P]phosphoenolpyruvate. This last result is expected in tissues showing metabolic flux largely in the glycolytic direction. The data indicate that in full-grown oocytes and embryos metabolic flux occurs largely in the gluconeogenic direction.     

Isolation of additional monoclonal antibodies directed against cell surface antigens of Myxococcus xanthus cells undergoing submerged development.

Thirteen additional monoclonal antibodies directed against cell surface antigens of Myxococcus xanthus cells undergoing submerged development were isolated and partially characterized. As measured by quantitative enzyme-linked immunosorbent assay, 10 of these antibodies recognized antigens common to both vegetatively growing cells and cells undergoing submerged development; 3 antibodies recognized antigens specific to developing cells. Five antigens were revealed as single bands on Western blots (immunoblots), and one produced multiple, diffuse bands characteristic of lipopolysaccharide.     

Surface tension gradients: feasible model for gliding motility of Myxococcus xanthus.

We propose that surface tension is the driving force for the gliding motility of Myxococcus xanthus. Our model requires that the cell be able to excrete surfactant in a polar and reversible fashion. We present calculations that (i) estimate the surface tension difference across a cell necessary to move the cell at the observed rate, which is less than 10(-5) dyn/cm, an extremely small value; (ii) estimate the rate of surfactant excretion necessary to produce the required surface tension difference, a rate that we conclude to be metabolically reasonable; (iii) predict the behavior of cells moving in close apposition to each other, and show that the model is consistent with observed behavior; and (iv) predict the behavior of cells moving in dense swarms. In an accompanying paper we present experimental evidence to support the surface tension model.     

Tactic behavior of Myxococcus xanthus.

With time-lapse videomicroscopy it was demonstrated that cells of Myxococcus xanthus are capable of directed (tactic) movement toward appropriate targets. Mutants that had lost A motility (J. Hodgkin and D. Kaiser, Mol. Gen. Genet. 171:177-191, 1979) were unable to show directed movement. Cells showed directed movement to polystyrene latex beads and to glass beads, as well as to clumps of Micrococcus luteus. This is consistent with other observations in an accompanying paper (M. Dworkin and D. Eide, J. Bacteriol. 154:437-442, 1983) that indicate that M. xanthus does not perceive chemical gradients.     

Comparative Intermediary Metabolism of Vegetative Cells and Microcysts of Myxococcus xanthus

Crude extracts of both vegetative cells and glycerol-induced microcysts of Myxococcus xanthus contained the following enzyme activities: phosphofructokinase, phosphoglucoisomerase, fructose-1,6-diphosphatase, fructosediphosphate aldolase, glyceraldehyde-3-phosphate dehydrogenase, phosphopyruvate carboxylase, citrate synthase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, malate dehydrogenase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, phosphoglucomutase, and uridine diphosphate glucose pyrophosphorylase. With the exception of isocitrate dehydrogenase, which was present at a fivefold higher concentration in microcysts, all activities in extracts from both types of cells were essentially equal. Hexokinase and pyruvate kinase could not be detected in extracts from either type of cell. Microcysts metabolized acetate at a lower rate than did vegetative cells. Most of this decrease was reflected in a substantial decrease in ability of microcysts to oxidize acetate to CO(2). In addition, microcysts and vegetative cells showed a different distribution of (14)C-label from incorporated acetate.     

Purification and properties of Myxococcus xanthus cell surface antigen 1604.

A cell surface antigen complex from Zwittergent-solubilized Myxococcus xanthus has been purified by immunoaffinity chromatography with monoclonal antibody (MAb) 1604 and by subsequent gel filtration. We propose that the cell surface antigen (CSA) 1604 complex participates in intercellular interactions. The apparent total molecular mass of the CSA 1604 complex is 200 kilodaltons (kDa), as determined by gel filtration and by electrophoresis and Western immunoblot probing with MAb 1604. The antigen epitope recognized by MAb 1604 is on a 51-kDa polypeptide. The CSA complex also contains 14% neutral carbohydrate and a 23-kDa polypeptide that lacks the 1604 epitope. The carbohydrate is most likely part of a lipopolysaccharide (LPS) associated with the CSA, because an MAb recognizing an O antigen epitope from the LPS of M. xanthus also reacted with CSA 1604 on Western immunoblots. Thus, the 200-kDa CSA complex consists of 97 +/- 6 kDa of protein and many associated LPS molecules. The LPS evidently produces the multiplicity of bands observed on Western immunoblots between 100 and 200 kDa. The association with LPS may contribute to the negative charge of the CSA 1604 complex, which has a pI of 4.3. The CSA was clustered on the surface of intact M. xanthus cells after labeling with MAb 1604 and immunogold. Furthermore, fractionation studies indicated that cells grown on a plastic surface had 50% of their total CSA 1604 in the cytosol, 39% in the membrane fraction, and 8% in the periplasm. Saturable binding studies with 125I-MAb 1604 indicated that there were 2,400 CSA 1604 sites per cell. The Kd for MAb 1604 binding to the cell was 9 nM.