Initiation of yeast sporulation of partial carbon, nitrogen, or phosphate deprivation.

In this paper we show that partial deprivation of a carbon source, a nitrogen source, or phosphate in the presence of all other nutrients needed for growth initiates meiosis and sporulation of Saccharomyces cerevisiae homothallic strain Y55. For carbon deprivation experiments, cells were grown in synthetic medium (pH 5.5) containing an excess of one carbon source and then transferred to the same medium containing different concentrations of the same carbon source. In the case of transfer to different acetate concentrations, the log optical density at 600 nm increased at the previous rate until the cells had used up all of the acetate, whereupon the cells entered a stationary phase and did not sporulate. The same was observed with ethanol. In contrast, at different concentrations of dihydroxy-acetone or pyruvate, cells grew at different rates and sporulated optimally at intermediate concentrations (50 to 75 mM). The response to galactose was similar but reflected the presence of a low-affinity galactose transport system and the induction of a high-affinity galactose transport system. Cells could also sporulate when a glucose medium ran out of glucose, apparently because they initiated sporulation during the subsequent lag period and then used the produced ethanol as a carbon source. For phosphate deprivation experiments, cells growing with excess ethanol or pyruvate and phosphate were transferred to the same medium containing limiting amounts of phosphate. First, they used up the intracellular phosphate reserves for rapid growth, and then they sporulated optimally when an intermediate concentration (30 muM) of phosphate had been added to the medium. For nitrogen deprivation experiments, cells grown with excess acetate, ethanol, or pyruvate and NH(4) (+) were transferred to the same medium from which all nitrogen had been removed. These cells sporulated well in acetate medium but poorly in ethanol and pyruvate media. However, the sporulation frequency in the latter media could be increased greatly by adding intermediate concentrations (1 mM) of the slowly metabolizable amino acids glycine, histidine, or phenylalanine. If one assumes that the sporulation response to partial deprivation of carbon-, nitrogen-, or phosphorus-containing compounds reflects control by a single metabolite, the intracellular concentration of this metabolite may decide at the START position (G1 phase) of the cell cycle whether a/alpha cells enter mitosis or meiosis.

Cholinesterase in the atherosclerotic intima and in fibroblast cultures.

Cholinesterase activity was present in the atheromatous plaque of the rabbit's atherosclerotic aorta. Cholinesterase activity was significantly increased in rat fibroblast cultures grown in the presence of hypercholesterolemic serum. Cholesterol ester synthesis in these cultures was inhibited by neostigmine, a cholinesterase inhibitor.

Cholinesterase in serum and low density lipoprotein of hyperlipidemic patients.

Cholinesterase activity in the low density lipoprotein fraction of serum is increased in types IIa, IIb and IV hyperlipoproteinemic patients, whereas only types IIb and IV show increases in serum cholinesterase activity. In obese patients, cholinesterase activity is increased both in the serum and low density lipoprotein fraction only when hyperlipidemia is present. Cholinesterase activity is also found to increase in proportion with increases in low density lipoprotein, cholesterol, and triglycerides both in the serum and low density lipoprotein fraction. We suggest on the basis of these findings that cholinesterase has a function in lipid and lipoprotein metabolism.