Structure and properties of the putrescine carbamoyltransferase of Streptococcus faecalis.

Ornithine and putrescine carbamoyltransferases from Streptococcus faecalis ATCC11700 have been purified and their structural properties compared. The molecular weight of native ornithine carbamoyltransferase, measured by molecular sieving, is 250 000. It is composed of six apparently identical subunits with a molecular weight of 39 000, as determined by cross-linking with the bifunctional reagent glutaraldehyde followed by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate. Using the same method, putrescine carbamoyltransferase is a trimer of 140 000 consisting of three identical subunits with a molecular weight of 40 000. Ornithine carbamoyltransferase displays a narrow specificity towards its substrate, ornithine. In contrast, putrescine carbamoyltransferase carbamoylates ornithine and several diamines (diaminopropane, diaminohexane, spermine, spermidine, cadaverine) in addition to its preferred substrate, putrescine, but with a considerable lower efficiency than for putrescine. The kinetic mechanism of putrescine carbamoyltransferase has been investigated. Initial velocity studies yield intersecting plots using either putrescine or ornithine as substrate, indicating a sequential mechanism. The patterns of protection of the enzyme by the reactants during heat inactivation as well as the results of product and dead-end inhibition studies provide evidence for a random addition of the substrates. The putrescine inhibition that is induced by phosphate does, however, suggest that a preferred pathway exists in which carbamoylphosphate is the leading substrate. The different kinetic constants have been established. The properties of putrescine carbamoyltransferase are compared to the known properties of other carbamoyltransferases. The evolutionary implications of this comparison are discussed.     

Phospholipids of Streptococcus faecalis

Autoradiograms of total lipid extracts from Streptococcus faecalis ATCC 9790, harvested in the stationary phase from a medium containing (32)P-orthophosphate, showed six major spots. The corresponding compounds were identified as diphosphatidylglycerol (possibly with a penta acyl structure); phosphatidylglycerol; a provisionally identified mixture of alanylphosphatidylglycerol and of the 2'-lysyl-derivative of phosphatidylglycerol; the 3'-lysyl-derivative of phosphatidylglycerol, probably together with some arginylphosphatidylglycerol; a diglucosyl derivative of phosphatidylglycerol; and a compound which was tentatively identified as the 2',3'-dilysyl derivative of phosphatidylglycerol.     

Folate metabolism in Streptococcus faecalis

The possibility that the inability of Streptococcus faecalis to utilize 5-methyltetrahydropteroylglutamate or pteroyltriglutamate might be due to permeability was investigated. Whereas the former was taken up by S. faecalis cells growing on pteroylglutamic acid, the latter was not. No subsequent conversion of the 5-methyltetrahydropteroylglutamate took place and accumulation, which was against a considerable concentration gradient, was inhibited by fluoride. It would thus appear to be an active process.     

Membrane-DNA attachment sites in Streptococcus faecalis cells grown at different rates

The M-band technique was used to assess the number of attachment points of DNA to the cell membrane of Streptococcus faecalis grown at three different rates. Cells were X irradiated in liquid nitrogen and then analyzed simultaneously for the introduction of double-strand breaks into the chromosome and the degree of removal of DNA from the cell membrane (M band). Consideration of the data from these experiments and of the topology of the bacterial chromosome resulted in a reevaluation of former quantitative models. Our results are consistent with a semiquantitative model in which the bacterial chromosome is organized around a core structure. We interpret our data to mean that the core is attached to the membrane and that the complexity of the core changes more drastically with growth rate than does the number of membrane-DNA attachment points. An alternative model in which RNA hybridizes with DNA containing single- and double-strand breaks is also discussed. In any event, the complexity of these interactions precludes a reliable estimate of the number of membrane-DNA attachment sites.     

Sodium-stimulated ATPase in Streptococcus faecalis.

We measured Na+-stimulated ATPase activity in a mutant of Streptococcus faecalis defective in the generation of proton motive force. The activity in membrane vesicles was 62.1 +/- 5.9 nmol of phosphate produced per min per mg of protein when cells were grown on medium containing 0.12 M Na+. Activity decreased as the concentration of Na+ in the growth medium decreased. The decrease in enzyme activity corresponded to the decrease in transport activity for Na+ in both whole cells and membrane vesicles. The effects of pH on both activities were identical. Thus, it is suggested that Na+ movement is mediated by this enzyme. Sodium extrusion and ATPase activity in the wild-type strain were markedly lower than those observed in the mutant strain. Elevated activities of both Na+ extrusion and Na+-stimulated ATPase could be detected in the wild-type strain when cells were grown in the absence of proton motive force. Thus, we propose that the level of ATPase is increased by dissipation of the proton motive force.     

Energization of membrane vesicles from the cells of glycolyzing bacterium Streptococcus faecalis]

Membrane fractions were isolated from Streptococcus faecalis cells of a glycolyzing microorganism, devoid of the respiratory chain, using the methods of osmotic shock of the protoplasts, ultrasonic treatment of the cells and ultrasonic treatment of the protoplasts. All fractions possessed the ATPase activity, the highest activity being observed in the fraction isolated by ultrasonication of the protoplasts. All preparations were estimated with respect to the presence of vesicles, formed by the "inside-out" and "inside-in" membranes, using ATPase as a marker of the membrane orientation. In the membrane fractions obtained by ultrasonication of the protoplasts, the "inside-out" vesicles were prevalent. ATP-dependent energization of the membranes, sensitive to the action of dicyclohexylcarbodiimide and tetrachlorotrifluoromethyl benzimidazole, was demonstrated by measuring the transport of the lipophylic anion of phenyldicarbaundecaborane and aniline naphthalene sulfonate fluorescence.     

Studies on Streptococcus faecalis enterotoxin

Streptococcus faecalis has been reported to cause food poisoning. Six strains of S. faecalis were tested for Sherman's criteria. These strains were non-hemolytic, DNase+ and Ent+. The enterotoxin was purified on Sephadex G-200 column and maximum activity was observed at 37 C and pH 7.0. Enterotoxin treated with trypsin and papain elicited very poor response to fluid accumulation. The sensitivity of all the strains against different antibiotics was determined. Strain 53 M was treated with acridine orange and ethidium bromide and a total of 44 Amps Strr and 3 Amps Strs mutants were tested for toxin production. Out of these only 4 were toxin negative, amongst which 3 were also DNase negative and 1 showed partial DNase activity.     

D-alanine carboxypeptidase from Streptococcus faecalis

A particulate D-alanine carboxypeptidase that can cleave the terminal residue of D-alanine from UDPMurNAc-L-ala-D-isoglu-L-lys-D-ala-D-ala was isolated from $\text{Streptococcus faecalis}$. The enzyme was inhibited by penicillin G non-competitively with a K_i of 0.8 μM.The carboxypeptidase was solubilized with Triton X-100 without loss of catalytic activity. In this form it could also be inhibited by penicillin G.     

Three-dimensional reconstruction of whole cells of Streptococcus faecalis from thin sections of cells.

A new ultrastructural technique has been developed to study the geometry of cell wall assembly in Streptococcus faecalis, which is believed to occur between pairs of raised bands located on the organism's surface. Three-dimensional reconstructions of these new regions of envelope growth are produced from the mathematical rotation (around a central axis) of various measurements taken from central, longitudinal thin sections of cells. These reconstructions can be used to calculate the surface area and volume of the septal and peripheral walls that were supposedly present in any given cell before sectioning. In an accompanying paper, it is shown how such surface and volume estimations, coupled with other measurements of length, thickness, and curvature, can be used to characterize a cycle of envelope growth in this organism. The validity of the assumptions used to reconstruct cells by rotation and the possible sources of error in using this technique are discussed.