Acetic acid/acetate inhibitory concentrations

The weak organic acids such as acetic acid and formic acid both have positive and negative effects on the bioethanol produetion proeess. In fermentations using S. cerevisiae NCYC 2592, an addition of aeetie acid in a concentration of 20 mM increased the ethanol produetivity (unpublished data). The low acetic acid concentrations (lower than 20 mM) did not have an impact on the yeast viability. At fermentations with higher acid concentration, the intracellular pH decreases, requiring plasma membrane ATPase to pump protons out of the cell. The depletion of ATP affected the biomass formation. In comparison with acetic acid, formic acid has a more severe inhibitory effect, which has also been observed in other biosynthesis processes, e.g. succinic acid formation. ... 

Phenyllactic and phenylpyruvic acids have an inhibitory effect on dopa decarboxylase and glutamic decarboxylase activity, but phenylalanine does not. Phenyl-acetic acid in equimolar concentrations had only half the inhibitory power of the two other metabolites. These findings might explain why low-phenylalanine diets restore pigmentation to normal in phenylke-tonuric individuals. 

Extraction procedures must be adjusted when separated anthocyanins will be tested in biological studies. We have found that the types of acids used for anthocyanin extraction as well as their residual concentrations in the final extract may affect the results obtained from biological tests. The growth inhibitory effect of anthocyanins on HT29 (human colonic cancer) cells may be overestimated if the residual acid in the extract exerts a toxic effect on the cells. Acetic acid residues in anthocyanin extracts showed less toxicity to HT29 cells than hydrochloric acid when samples were prepared under the same extraction procedure and subjected to the same tests on HT29 cells. In addition, the procedure to remove acids affected the acid residual concentration as well in final anthocyanin extracts, with lyophilization being more successful than rotary evaporation. 

Fraenkel et al. (17), who isolated mutant strains which had lost the ability to grow on glycerol, succinate, or acetate but grew normally on hexoses or pentoses. These organisms were shown to be deficient in a specific FDPase, which could be distinguished from the nonspecific acid hexosephosphatase present in both mutant or wild-type strains by the fact that the latter was present in the periplasmic space (86) and did not require a divalent metal cation. The properties of the specific FDPase were confirmed with a partially purified preparation (87) the E. coli enzyme was shown to be highly specific for FDP and to be active with very low concentrations of this substance. The requirement for a divalent cation was satisfied by Mg2+, which was far more effective than Mn2+ other divalent cations were either inactive or inhibitory. The partially purified enzyme showed optimum activity at pH 7.8, with very little activity below pH 7 or above pH 9. The enzyme resembled mammalian and Candida FDPases in its sensitivity to low concentrations of AMP it was approximately 50% inhibited at an AMP concentration of 2.5 X 10-° M. 

The effects of triethyllead acetate or tetraethyllead, as well as an inorganic lead nitrate Pb(NC>3)2 on human erythrocytic 5-aminolevulinic acid dehydratase activity was investigated. There was no discernible inhibitory effect of tetraethyllead at any concentration, with and without pre-incubation. Lead nitrate is a much more potent inhibitor of 5-aminolevulinic acid dehydratase activity (0.77 pM) than triethyllead acetate (130.37 pM)141. 

The significant influence of carboxylic acid on these reactions prompted a fundamental investigation into its role in the aerobic oxidation of 1-phenylethanol catalyzed by 44a (0.5 mol %) [80]. At low concentrations (<0.62 mol %), acetic acid has a beneficial effect on the reaction rate (Fig. 3a). Beyond this concentration, acetic acid exhibits an inhibitory effect. Acetic acid also influences the catalyst stability (Fig. 3b). In the absence of acetic acid, the reaction proceeds only to low levels of conversion. At 0.75 mol % acetic acid, the reaction begins with a high initial rate, but the time-course deviates from the expected first-order dependence on [alcohol] (Fig. 3b). The first-order dependence observed when [AcOH] is > 2mol% suggests that the catalyst is more stable (albeit somewhat less active) under these conditions. 

The studies presented herein should be considered only semiquanti-tative in nature since it has been necessary to make several simplifying assumptions in developing the model, and reliable values for many of the parameters are not available. Reasonable estimates of /I = 0.4 day Kg = 0.0333 mmole/liter, and Yx/a = 0.02 mole/mole were made from the data of Lawrence and McCarty (5). For acetic acid, Yco2/x and Ych4/x are equal and were determined from the basic stoichiometry (Equation 3) as 47.0 moles/mole. An order of magnitude estimate of Ki = 0.667 mmole/liter was made using the 2000-3000 mg/liter of total volatile acids that Buswell (6) considers to be inhibitory. The estimates for Kg and Kj are not as reliable as those for Jl and the yield constants because Kg and Ki must be expressed as concentrations of unionized acid. 

Intemasal delivery of peptide and protein drugs is severely restricted by pre-systemic elimination due to enz5miatic degradation or mucociliary clearance and by the limited extent of mucosal membrane permeability. a-CyD has been shown to remove some fatty acids from nasal mucosa and to enhance the nasal absorption of leuprolide acetate in rats and dogs. The utility of chemically modified CyDs as absorption enhancers for peptide drugs in rats has been demonstrated. For example, DM-P-CyD was shown to be a potent enhancer of insulin absorption in rats, and a minimal effective concentration of DM-(3-CyD for absorption enhancement exerted only a mild effect on the in vitro ciliary movement.The scope of interaction of insulin with CyDs is limited, because CyDs can only partially include the hydrophobic amino acid residues in peptides with small stability constants. Under in vivo conditions, these complexes will readily dissociate into separate components, and hence the displacement by membrane lipids may further destabilize the complexes. The direct interaction of peptides with CyDs is therefore of minor importance in the enhancement of nasal absorption. Of the hydrophilic CyDs tested, DM- 3-CyD had the most prominent inhibitory effect on the enzymatic degradation of both BLA and insulin in rat nasal tissue homogenates. Because of the limited interaction between peptides and CyDs,... 

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