Fermentative capacity after cold storage of baker's yeast is dependent on the initial physiological state but not correlated to the levels of glycolytic enzymes.

Growth and starvation of baker's yeast was monitored by on-line microcalorimetry and cells originating from four different physiological states were stored at low temperature (4 degrees C) for up to 26 days. The different physiological states were designated F (respiro-Fermentative phase of growth), R (initial Respiratory phase of growth), -N (non-growing state because of Nitrogen depletion), and -NC (non-growing state because of both Nitrogen and Carbon depletion). The cells were tested before and after cold storage for their fermentative capacity, and characterised by 2D gel analysis (and subsequent quantitative silver staining and image analysis with software PDQUEST) for their levels of six enzymes of the glycolytic pathway (hexokinase 2 (Hxk2p), fructose bisphosphate aldolase (Fba1p), glyceraldehyde-3-phosphate dehydrogenase (Tdh3p), enolase A (Enolp), enolase B (Eno2p), and triose phosphate isomerase (Tpi1p)) and two enzymes of the fermentative branch (pyruvate decarboxylase (Pdc1p) and alcohol dehydrogenase (Adh1p)). The enzymes Hxk2p, Tdh3p, Eno2p, Pdc1p and Adh1p were down-regulated by 25-80% during the transition between the F and R states. During the transition to non-growing states (-N and -NC states), the levels of Hxk2p, Tdh3p and Eno2p were further reduced. However, after cold storage, the glycolytic and fermentative enzymes of the different physiological states were expressed to the same extent. In contrast, the fermentative capacity differed between the states; the R-state cells were superior compared to cells from the other states tested and preserved more than 50% of their initial fermentative capacity (6 mmol ethanol per gram dry weight and hour). Our data therefore clearly demonstrate that persistence of fermentative capacity during total starvation at low temperature after as long as 1 month is strongly dependent on the physiological state from which the cells originate. However, the level of expression of the glycolytic enzymes could not explain the difference in fermentative capacity of the different physiological states after cold storage.

Biosynthesis of prostaglandin D2. 1. Formation of prostaglandin D2 by human platelets.

Formation of prostaglandin D2 (PGD2) during the aggregation of platelets was determined, employing a specific bioassay. PGD2 was synthesized in human platelet rich plasma (PRP) in response to thrombin, collagen and epinephrine. Indomethacin pretreatment abolished the biosynthesis of PGD2. When thrombin treated PRP was incubated for different periods of time and denatured in the presence of SnCl2 to prevent the formation of PGD2 from endoperoxides during the extraction procedure, PGD2 formation was noted within the first minute of incubation and reached a peak level after 4 minutes. PGD2 from thrombin stimulated PRP was conclusively identified by gas chromatography-mass spectrometry. The formation of PGD2 during platelet aggregation could represent a mechanism of feedback inhibition of aggregation.