Search PubMed⌕ Search

Biomedical subjects

D P Fan

Publications and source records attributed to D P Fan.

At least 55 records · Page 3Linked to original sources
PubMed1975

Passage of a membrane protein through the walls of toluene-treated Bacillus megaterium cells.

Based on autoradiographic and microscopic evidence, it seems likely that a membrane protein essential for peptidoglycan synthesis can be extracted from uhlysed toluene-treated Bacillus megaterium cells. Furthermore, this protein can be added back to the membrane through the wall to reconstitute peptidoglycan synthesis. Autoradiograms also show that peptidoglycan is synthesized from externally added nucleotide precursors over the entire length of the toluene-treated bacterial. The amounts of peptidoglycan made is to small to be visible by thin section electron microscopy.

Autoradiography↗
PubMed1975

Mode of cell wall synthesis in gram-positive bacilli.

Ultrastructural experiments on plasmolyzed cells suggested that the information for the position and orderly synthesis of septa is not determined by the attachment of cell membrane to previously formed wall. These experiments, in conjunction with others on cells disrupted by the freeze-fracture technique, are most consistent with wall growth over the entire surface of the rods, with wall material gradually moving from a position next to the cell membrane to a position at the outer surface of the cell.

Bacillus subtilis↗
PubMed1975

Further characterization of a non-essential mutator gene in Escherichia coli K-12.

The properties of mutR, a mutator closely linked to thyA, have been further characterized. We have found that the mutator gene is carried on a specialized transducing phage (lambdapcI857 thyA) generated by the excision of lambdacI857 integrated at a secondary attachment site between lysA and thyA. We present three lines of evidence indicating that mutR is a nonessential gene. (i) Deletions of the mutator can be found amoung survivors of heat induction of lambdacI857 when the phage is integrated between lysA and thyA. (ii) Mutations in mutR can be induced with the frameshift mutagen ICR-191. (iii) An amber mutant in mutR has been found. Viable strains could be made by combining the mutator with polB, polA polR, ligts7, and uvrA mutations. The mutator was still able to increase the spontaneous mutation frequency in these genetic backgrounds. When the reversion patterns of a series of well-characterized trpA mutations were analyzed, the results suggested that mutR is more efficient at causing transitions than transversion mutations.

Base Sequence↗
PubMed1974

Cell wall turnover at the hemispherical caps of Bacillus subtilis.

Cell walls made by Bacillus subtilis bacteria grown in D(2)O medium have buoyant densities in CsCl which are different from walls made by cells grown in H(2)O medium. Cell wall turnover was studied by measuring the change in wall buoyant density after a B. subtilis culture was shifted from growth in D(2)O medium to aeration in H(2)O medium. Walls from the hemispherical caps were isolated after preferential digestion of wall from the cylindrical regions using the B. subtilis autolytic amidase. The walls from the polar regions were found to turn over extensively.

Amidohydrolases↗
PubMed1973

Mutant of Bacillus subtilis with a temperature-sensitive autolytic amidase.

A procedure incorporating a petri plate assay for autolysins has been developed for the systematic isolation of mutants with a temperature-sensitive autolytic amidase. We suggest maa as the name for the gene for this enzyme. One such mutant has been characterized as having a heat-sensitive amidase in a variety of studies with both crude autolysin preparations and purified amidase solutions.

Alanine↗
PubMed1973

Micrococcus lysodeikticus bacterial walls as a substrate specific for the autolytic glycosidase of Bacillus subtilis.

The Bacillus subtilis 168 autolytic glycosidase degrades Micrococcus lysodeikticus cells or cell walls, whereas the B. subtilis autolytic amidase does not. The criteria used to establish this fact included: the determination of chemical bonds broken, heat-inactivated kinetics, pH dependence curves, and the physical separation of glycosidase from amidase. The physical separation involved LiCl elution from two different ion-exchange materials, walls from B. subtilis 168 strain betaAO, and walls from mutant strain betaA173 derived from strain betaAO. No evidence was obtained for B. subtilis vegetative bacteria making any more autolysins than one autolytic amidase and one autolytic glycosidase.

Amidohydrolases↗
PubMed1972

Ultrastructural studies on a mutant of Bacillus subtilis whose growth is inhibited due to insufficient autolysin production.

The growth of Bacillus subtilis mutant betaA177 can be inhibited under special conditions in which not enough autolytic enzymes are produced for optimal growth. Electron microscopy studies show that during growth inhibition there is localized thickening of the cell wall at positions where cells bend. A model is proposed to explain this result. Rapid growth can be restored by adding lysozyme or a B. subtilis autolysin mixture to a growth-inhibited betaA177 culture. Such addition reduces the localized wall thickening and causes other changes in surface morphology which are described and discussed. Septum formation seems to be relatively less inhibited than cell elongation when lytic enzyme levels are reduced. Measurements were made demonstrating that walls at ends of cells are morphologically different from walls at sides of cells in cultures of betaA177 growing at 51 C.

Autolysis↗
PubMed1972

New centrifugation technique for isolating enzymes from large cell structures: isolation and characterization of two Bacillus subtilis autolysins.

Bacillus subtilis cell walls can be centrifuged through a linear gradient of 0 to 2 m LiCl and 10 to 25% sucrose so that different autolysins are removed by different salt concentrations and banded in separate positions as the walls pass through the gradient. Using this technique we have found that B. subtilis cell walls are isolated with two autolytic enzymes attached. One autolysin, a glycosidase, can be eluted from walls with 0.5 m LiCl, has a pH optimum between 5 and 8, is relatively heat-sensitive, and has a molecular weight of 60,000. The other autolysin, an alanine amidase, can be eluted from walls with 1.5 m LiCl, has a pH optimum around 8, is relatively heat-stable, has a molecular weight of 35,000, and is present in quantities ten times greater than the glycosidase.

Alanine↗
PubMed1971

Mutant of Bacillus subtilis demonstrating the requirement of lysis for growth.

A temperature-sensitive mutant of Bacillus subtilis which has impaired ability to autolyze was isolated. The growth rate of mutant cells at high temperature can be increased by the addition of egg-white lysozyme or a B. subtilis autolysin. Experiments with this mutant show that lysis is essential for cell growth.

Bacillus subtilis↗
PubMed1970

Cell wall binding properties of the Bacillus subtilis autolysin(s).

Cell walls isolated from exponentially growing Bacillus subtilis have autolysin(s) attached to them. An autolysin can be released from the walls by incubation at 0 C with 3 m LiCl. The enzyme can reattach to walls when the salt concentration is reduced. The bound enzyme cannot be removed or destroyed by washing the walls with 8 m urea at 0 C. The binding of free enzyme to walls at 0 C can take place normally in the presence of 2 m urea.

Autolysis↗
PubMed1970

Autolysin(s) of Bacillus subtilis as dechaining enzyme.

Bacillus subtilis bacteria grow exponentially as long filaments in well-aerated cultures at 48 C. These filaments are chains of cells which can become unlinked when a B. subtilis autolysin or egg white lysozyme is added to the culture medium.

Bacillus subtilis↗