A simple spectrophotometric method for determining proton release from yeast cells

Visual and simple determination of glucose-induced acidification by yeast cells: application to rapid cytotoxicity test

This study demonstrated that glucose-induced proton release from yeast cells was more sensitive to various inhibitors than cell proliferation. In this study the inhibition of glucose-induced proton release was determined on the basis of color change of pH indicator, methyl red, from pH 5 to pH6 at cell density of 2.5 × 10⁷ cells/ml. When yeast cells were incubated with the inhibitors of glucose intake, glycolysis, and plasma membrane H ⁺ -ATPase for 1 h, these cytotoxic effects were observed by following the change in absorbance at 527 nm due to methyl red for 5 min. The cytotoxic effects of heavy metal ions, detergents and quinones were observed in the same manner. The above method was superior in sensitivity and measurement time to cell proliferation measurement that required 9 h. This visual cytotoxicity test (methyl red test) is expected to be useful as simple and rapid cytotoxicity test with yeast cells.

Proton production and consumption pathways in yeast metabolism. A chemostat culture analysis

In this investigation, a method for the accurate quantitative determination of net proton production or consumption in biological cultures has been devised. Cells are cultured under constant pH conditions. The specific rate of proton production or consumption by the culture (qH+, mmol h-1 per g biomass) is proportional to the mmol of base or acid required to maintain constant pH per unit time, and this equivalence is independent of the buffering capacity of the culture medium. The above method has been applied to chemostat cultures of Candida utilis growing on glucose or glycerol as carbon source, and different nitrogen sources. The results indicate that the nitrogen assimilation pathway alone determines the value of qH+, and a fixed stoichiometric relationship between nitrogen uptake rate qN (meq h-1 per g biomass) and qH+ has been found for each nitrogen source employed. Thus, qH+/qN values of +1, 0 and -1 were found for ammonium ions, urea and nitrate respectively. Under oxidative metabolism, the contribution of carbon catabolism to the value of qH+ was undetectable. Sine qN may be related to growth and production of type 1 compounds in fermentation processes, the parameter qH+ was incorporated into a model of growth and energy metabolism in chemostat culture (Castrillo and Ugalde, Yeast 10, 185 - 197, 1994), resulting in adequate simulations of experimentally observed culture performance. Thus, it is suggested that qH+ may be employed as a simple and effective control parameter for biotechnological processes involving biomass-related products.

Intracellular ATP in a glucosephosphate isomerase mutant of Saccharomyces cerevisiae

The degree of ATP depletion caused by glucose in a glucosephosphate isomerase-deficient strain of Saccharomyces cerevisiae was determined. Even in the presence of a sugar normally fermentable by the mutant, the addition of glucose can decrease the intracellular ATP, depending on the competition of the sugars for transport and subsequent phosphorylation. For both parent and mutant cells, a correlation exists between the calculated velocity of ATP formation or ATP consumption during the utilization of different concentrations of sugars and the experimental intracellular ATP level. For initially resting yeast cells, a rate increase of 35 mumol per min per g ATP was calculated to increase the intracellular level of this nucleotide by 1 mumol per g cell mass.

Rapid spectrophotometric pH measurements based on the dual-wavelength technique

A spectrophotometric method for the measurement of pH in solutions of lidocaine hydrochloride (Xylocaine) for injection is presented. 4-Nitrophenol is used as an indicator for determinations of pH in the range 6.5-7.0. The method was found to be faster than the conventional potentiometric method, mainly due to the utilization of a computer-controlled photodiode array spectrophotometer for the measurements. A further advantage with the spectrophotometric method is that errors arising from varying liquid junction potentials are avoided.