No abstract

Fully acylated lipoteichoic acid (LTA) isolated from Streptococcus faecalis ATCC 9790 (S. faecium) inhibited autolysis of walls from the same organism at concentrations (1.0 to 1.5 nmol of LTA per mg of wall) comparable to those found in intact cells. Partially deacylated LTA isolated from S. faecalis or chemically deacylated LTA failed to inhibit significantly in the same concentration range. Beef heart cardiolipin and commercially obtained dipalmitoyl phosphatidyl glycerol were also found to inhibit wall autolysis in S. faecalis. Chemical deacylation of beef heart cardiolipin also removed the inhibitory activity of this molecule. Lipid fractions isolated from S. faecalis that inhibited wall autolysis were: diphosphatidyl glycerol (cardiolipin), phosphatidyl glycerol, aminoacyl phosphatidyl glycerol, and a neutral lipid fraction. Glycolipids were not found to be effective inhibitors. The possible role of LTA and/or certain lipids as regulators of cellular autolytic activity is discussed.

Autolysis of intact cells of Streptococcus faecalis was inhibited to a greater extent by phospholipids than by lipoteichoic acid, suggesting a possible difference in the accessibility of native autolysin to these substances.

Vegetative amoeboid cells of the cellular slime mould, Dictyostelium discoideum NC-4, are very resistant to gamma-radiation . Mutant strains have been isolated which are significantly more radiosensitive . Studies were conducted to measure division delays and other growth responses after irradiation of strain NC-4 and two mutant strains . Some division of non-surviving (non-colonyforming) cells was observed in all strains . Total cell populations (surviving plus non-surviving cells) in all three strains showed essentially equivalent division-delay responses . However, surviving cells of the mutant strains revealed division delays that were much longer than those of the total cell populations . A model is proposed to interpret these results . A basic premise of the model is that, if more time is allowed for repair of potentially lethal damage incurred by the sensitive strains, cellular survival will be greater . Support for this model was obtained by producing artificially long delays in populations consisting of irradiated mutant cells . Increases in survival were observed for the sensitive strains but not for strain NC-4 .

Changes in the levels of specific activity of two enzymes believed to be involved in developmental regulation were observed after irradiating differentiating cells of Dictyostelium discoideum. Stimulation of the levels of specific activity of alkaline phosphatase occured after irradiation at the beginning of development and at the end of the aggregation period, but not after irradiation at the beginning of aggregation. A stimulation in UDP-glucose pyrophosphorylase specific activity was also observed, but to a lesser extent and only after irradiation at the end of aggregation. Dose-dependent delays in the appearance of peaks of specific activity were noted. The delay per unit dose was less when irradiation took place at the beginning of development as opposed to the beginning or end of the aggregation period. Radiation-induced delays in progression through visible developmental stages were almost identical to delays in enzyme appearance. Other radiation effects on morphogenesis included the induction of a migratory slug phase.