Acetate, active from lactate

Following an abrupt transition of P. pentosaceum from anaerobic to aerobic metabolism (10 pM O2), the growth rate increases at first, but the formation of acetate from lactate and glucose is slowed down, propionate formation is completely repressed and pyruvate is accumulated in the medium (van Gent-Ruijters et al, 1976 Schwartz et al, 1976). A decrease in the activities of the citric acid cycle enzymes malate dehydrogenase, fumarase and NADH oxidase, lactate oxidase, NADH-dependent fiimarate reductase, lactate-dependent nitrate reductase is observed upon the transition from anaerobic to aerobic (10 pM O2) metabolism (van Gent-Ruijters, 1975). 

The concept of using colloids stabilized with chiral ligands was first applied by Bonnemann to hydrogenate ethyl pyruvate to ethyl lactate with Pt colloids. The nanoparticles were stabilized by the addition of dihydrocinchonidine salt (DHCin, HX) and were used in the liquid phase or adsorbed onto activated charcoal and silica [129, 130]. The molar ratio of platinum to dihydrocinchonidine, which ranged from 0.5 to 3.5 during the synthesis, determines the particle size from 1.5 to 4 nm and contributes to a slight decrease in activity (TOF = l s ). In an acetic acid/MeOH mixture and under a hydrogen pressure up to 100 bar, the (R)-ethyl lactate was obtained with optical yields of 75-80% (Scheme 9.11). 

Similar tracer studies have been carried out using smaller compounds, such as acetate, although the interpretation of the results obtained from these biosynthetically more remote precursors is difficult, especially when they are used in the intact animal. Thus C -labeled carbonate, acetate-I-C, and acetate, butyrate, and caproate labeled at C-2, injected intravenously into lactating cows, produced lactose having similar specific activities in the D-glucose and D-galactose residues. This observation has been con-... 

---