Search PubMed⌕ Search

Biomedical subjects

B E Wright

Publications and source records attributed to B E Wright.

At least 91 records · Page 5Linked to original sources
PubMed1971

Nucleotide metabolism during differentiation in Dictyostelium discoideum.

Energy metabolism in Dictyostelium discoideum was studied by following the incorporation of [(3)H]adenine and [(32)P]Pi into the intracellular adenine nucleotides at two stages of differentiation. That the levels of nucleotides measured represented levels present in vivo was shown by demonstrating that the concentrations determined from cells quickly frozen in liquid nitrogen were identical to those from cells harvested and subsequently killed in perchloric acid. In addition, significant compartmentalization among the nucleoside triphosphates was not observed after 30 min, since uridine triphosphate, guanosine triphosphate, and adenosine triphosphate (ATP) were at radioactive equilibrium after exposure to [(32)P]Pi. At the sorocarp stage of differentiation, the dominant role of adenylate kinase activity is indicated by the observations that (i) adenylate kinase activity was found to be present, (ii) the specific radioactivities of the beta- and gamma-phosphates of ATP were equal, (iii) the increase in specific radioactivity of adenosine diphosphate was one-half that of ATP in the presence of [(32)P]Pi, and (iv) the steady-state equilibrium constant calculated (0.69) from the nucleotide levels equaled that of the apparent equilibrium constant reported in the literature (0.70). By using the same criteria, adenylate kinase activity was not the predominant reaction establishing the adenine nucleotide levels in cells at the pseudoplasmodium stage of differentiation.

Adenine↗
PubMed1971

Effects of adenosine 3',5'-monophosphate and adenosine 5'-monophosphate on glycogen degradation and synthesis in Dictyostelium discoideum.

Data are presented demonstrating that the presence in vivo of adenosine 3',5'-monophosphate (3',5'-AMP) causes a rapid depletion of glycogen storage material in the cellular slime mold. The effect of adenosine 5'-monophosphate (5'-AMP) is twofold, stimulating both glycogen degradation and synthesis. In pseudoplasmodia, cell-free extracts appear to contain at least two species of glycogen phosphorylase, one of which is severely inhibited by glucose-1-phosphate and another which is only partially inhibited by this hexose-phosphate. In some cases, 5'-AMP partially overcomes the inhibition by glucose-1-phosphate. Data presented here also indicate the existence of two forms of glycogen synthetase, the total activity of which does not change during 10 hr of differentiation from aggregation to culmination. During this period there is a quantitative conversion of glucose-6-phosphate-independent enzyme activity to glucose-6-phosphate-dependent activity. It is suggested that one effect of 3',5'-AMP is closely related to enzymatic processes involved in the rapid conversion of glycogen to cell wall material and other end products accumulating during sorocarp construction.

Adenine Nucleotides↗
PubMed1970

Selection of a single antibody-forming cell clone and its propagation in syngeneic mice.

A single antibody-forming cell clone has been selected from primed mice by sequential transfer of limited numbers of spleen cells into irradiated syngeneic mice. The original spleen cell donors had been immunized with dinitrophenylated bovine gamma globulin. Specific antibody molecules in sera of recipient mice were separated by isoelectric focusing on polyacrylamide gels and visualized by (131)I-hapten binding and autoradiography. This method provided a marker for antibody-forming cells derived from a single cell clone. This report describes the history of one clone of cells (E9) producing IgG antibody to dinitrophenyl. Clone E9 is long-lived and has been maintained for five transplant generations (over 6 months) by serial transfer of spleen cells into irradiated syngeneic mice. Clone E9 has the following properties: (1) Antibody production strictly depends on antigen, presented either in vivo or in vitro; (2) Induction of E9 anti-dinitrophenyl shows specificity for the carrier protein; (3) Antibody is produced in amounts (2-3 mg/ml serum) comparable with myeloma-protein production by murine plasmacytomas; (4) In the absence of antigen, memory cells have a lifetime exceeding 28 days.

Animals↗
PubMed1970

Partial purification and characterization of glycogen phosphorylase from Dictyostelium discoideum.

Glycogen phosphorylase was isolated from cells of Dictyostelium discoideum in the culmination stage of development and purified 35-fold. The enzyme had a pH optimum of 6.9 and contained sulfhydryl groups essential for activity. The K(m) values for phosphate and glycogen were 3 mm and 0.06% (w/v), respectively. No dependence on, or stimulation by, any nucleotide was observed and a wide variety of nucleotides and glycolytic intermediates did not inhibit the enzyme. Nucleotide sugars competitively inhibited the enzyme. Guanosine diphosphoglucose and adenosine diphosphoglucose were the most effective, and uridine diphosphoglucose was the least effective of the nucleotide sugars tested. The specific activity of glycogen phosphorylase increased from about 0.004 unit per mg of protein in aggregating cells to about 0.024 unit per mg in culminating cells, and then decreased during sorocarp formation. This increase in enzyme specific activity during the starvation and aging of the system can account for the increased rate of glycogen degradation during this period of development. Amylase specific activity, measured at pH 4.8 and 6.9, varied between 0.005 and 0.013 unit per mg of protein during all stages of development.

Acetone↗
PubMed1968

Stability in vitro of uridine diphosphoglucose pyrophosphorylase in Dictyostelium discoideum.

The stability of uridine diphosphoglucose pyrophosphorylase was examined in extracts prepared at different stages of development in Dictyostelium discoideum. In the early stages, the kinetics of inactivation were nonlinear, and, therefore, it was not possible to determine the specific enzyme activity. In the later stages of development, the enzyme was stable, but it could be rapidly inactivated by a heat-labile inhibitor present in extracts prepared at an early stage.

Kinetics↗
PubMed1966

Multiple causes and controls in differentiation.

In this article the process of differentiation is analyzed, cell wall synthesis in a cellular slime mold being used as a model system. The causes and levels of control responsible for morphogenesis are many and complex; their interdependence must be understood in order to interpret their individual roles in the regulation of mor phogenesis.

Cell Differentiation↗