Acidification power: indicator of metabolic activity and autolytic changes in Saccharomyces cerevisiae

Biotechnological aspects of membrane function

An overview is given of the biotechnological utilizability of various features of cell membranes. Techniques are given that describe how to make use of the barrier and transport functions of membranes for biotechnological purposes, ranging from cell permeabilization and construction of immobilized biocatalysts to manipulating excretion and uptake properties of the membranes by various methods. Glucose transporters, iron-transporting membrane systems, and pumps engaged in pleiotropic drug resistance are treated in more detail as particularly biotechnologically important membrane proteins.

Effects of the physiological state of five yeast species on H(+)-ATPase-related processes

Effects of starvation and glucose preincubation on membrane potential, ATPase-mediated acidification and glutamic acid transport were studied in yeast species Saccharomyces cerevisiae, Schizosaccharomyces pombe, Dipodascus magnusii, Lodderomyces elongisporus and Rhodotorula gracilis. The membrane potential was highest after preincubation with glucose in all species but L. elongisporus and R. gracilis. In all cases the membranes were depolarized in the presence of 20 mmol/L KCl and hyperpolarized with 50 mumol/L diethylstilbestrol (DES). The extracellular acidification caused by addition of glucose was highest after preincubation with glucose in all cases except in R. gracilis where there was none. In all cases except in R. gracilis addition of KCl caused a marked increase in the acidification rate. Addition of DES with glucose caused a large decrease in rate in S. cerevisiae but had much less effect on the other species. Transport of glutamic acid was clearly increased after pretreatment with glucose in S. cerevisiae, S. pombe and D. magnusii (mainly due to enhanced synthesis of the carrier) but actually decreased in R. gracilis and L. elongisporus. Addition of DES had an inhibitory effect in all species but much more pronounced in S. cerevisiae and S. pombe than in others. In general, both the acidification and the transport of glutamate were enhanced after preincubation with glucose but much more so in the semianaerobic species, such as S. cerevisiae, than in the strict aerobes (R. gracilis) where the effect was occasionally negative. There was no relationship between the ATPase-mediated acidification and the membrane potential.

Membrane transport in an osmotically fragile mutant of Saccharomyces cerevisiae

Transport properties of the osmotically fragile strain VY1160 of Saccharomyces cerevisiae were compared with those of the parent S288c strain. Mediated diffusion of 6-deoxy-D-glucose was practically unaffected; membrane-potential-dependent transport of D-glucosamine was very much depressed in the fragile strain. The H+-driven transport of L-lysine and L-proline, as well as that of the hitherto uninvestigated D-glucose-6-phosphate, were also very depressed. 2-Deoxy-D-glucose transport displayed slightly different kinetic parameters. Primary H+ extrusion by the plasma membrane H-ATPase was not diminished although the ATP-splitting activity was depressed by about 50%. The overall proton-motive force (pmf) of the fragile mutant at pH 5.5 was only 20 mV while in the parent strain it was 108 mV. In parallel with this, spontaneous acidification of the external medium (a CO2-associated event) was only about 2% of that in the parent strain. The defect in this, together with the inability to stimulate transport protein synthesis by glucose, may account for the generally poorer transport performance of the fragile mutant.

Intracellular pH distribution and transmembrane pH profile of yeast cells

The pH-dependent fluorescence excitation of fluorescein located intracellularly and in the vicinity of cells of the yeast Saccharomyces cerevisiae and Endomyces magnusii was used to obtain local pH values at a linear resolution 0.2 micron. Cells suspended in water or in a diluted (5 mM) acidic buffer had a relatively alkaline interior (about 7.0-7.5) with pH decreasing gradually toward the periphery and further out through the cell wall to the value of the bulk solution. In slightly alkaline weak buffers the cells also showed an alkaline center and a slightly acidic ring-shaped area, but the peripheral region close to the membrane was again alkaline with pH increasing toward the bulk solution. The heterogeneity of intracellular pH was reduced or nearly abolished in starved or antimycin-treated cell. Suspension of cells in strong (200 mM) buffer resulted within 15-20 min in a nearly homogeneous pH pattern throughout the cell, attaining pH values of 5.5-7.5, depending on the pH of the buffer. Addition of glucose with concomitant pH decrease of the extracellular medium did not change appreciably the intracellular pattern for 20-30 min, except with diethylstilbestrol (inhibitor of proton-extruding ATPase) when the cell became more acidic. It appears that the delta pH measurements between the cell as a whole and the bulk solution (as are used for the calculation of the electrochemical potential of protons in proton-driven transports) are not substantiated, the probable pH difference across the plasma membrane being substantially smaller than previously supposed.