Biochemical basis of mitochondrial acetaldehyde dismutation in Saccharomyces cerevisiae

As reported previously, Saccharomyces cerevisiae cells deficient in all four known genes coding for alcohol dehydrogenases (ADH1 through ADH4) produce considerable amounts of ethanol during aerobic growth on glucose. It has been suggested that ethanol production in such adh0 cells is a corollary of acetaldehyde dismutation in mitochondria. This could be substantiated further by showing that mitochondrial ethanol formation requires functional electron transport, while the proton gradient or oxidative phosphorylation does not interfere with reduction of acetaldehyde in isolated mitochondria. This acetaldehyde-reducing activity is different from classical alcohol dehydrogenases in that it is associated with the inner mitochondrial membrane and also is unable to carry out ethanol oxidation. The putative cofactor is NADH + H+ generated by a soluble, matrix-located aldehyde dehydrogenase upon acetaldehyde oxidation to acetate. This enzyme has been purified from mitochondria of glucose-grown cells. It is clearly different from the known mitochondrial aldehyde dehydrogenase, which is absent in glucose-grown cells. Both acetaldehyde-reducing and acetaldehyde-oxidizing activities are also present in the mitochondrial fraction of fermentation-proficient (ADH+) cells. Mitochondrial acetaldehyde dismutation may have some significance in the removal of surplus acetaldehyde and in the formation of acetate in mitochondria during aerobic glucose fermentation.

Ethanol formation in adh0 mutants reveals the existence of a novel acetaldehyde-reducing activity in Saccharomyces cerevisiae

A strain of Saccharomyces cerevisiae has been constructed which is deficient in the four alcohol dehydrogenase (ADH) isozymes known at present. This strain (adh0), being irreversibly mutated in the genes ADH1, ADH3, and ADH4 and carrying a point mutation in the gene ADH2 coding for the glucose-repressible isozyme ADHII, still produces up to one third of the theoretical maximum yield of ethanol in a homofermentative conversion of glucose to ethanol. Analysis of the glucose metabolism of adh0 cells shows that the lack of all known ADH isozymes results in the formation of glycerol as a major fermentation product, accompanied by a significant production of acetaldehyde and acetate. Treatment of glucose-growing adh0 cells with the respiratory-chain inhibitor antimycin A leads to an immediate cessation of ethanol production, demonstrating that ethanol production in adh0 cells is dependent on mitochondrial electron transport. Reduction of acetaldehyde to ethanol in isolated mitochondria could also be demonstrated. This reduction is apparently linked to the oxidation of acetaldehyde to acetate. Preliminary data suggest that this novel type of ethanol formation in S. cerevisiae is associated with the inner mitochondrial membrane.

Nursing Education Application of a Computerized Nursing Expert System

Nurse educators are required to be knowledgeable about a wide variety of complex health care problems in order to provide quality education. At the same time, they are given a multitude of other responsibilities such as participating in scholarly activity, advising students, maintaining an active role in nursing practice, and performing community service. These educators must find innovative ways to present current lectures while at the same time meeting their other obligations. The use of Creighton Online Multiple Modular Expert System (COMMES), a computerized decision support consultant, was evaluated as a technique for faculty use in developing and organizing new lecture content. The study found that COMMES was beneficial as a systematic prompt for lecture content, as a tool for organizing content, and as a means to verify completeness of lecture material.

Activation of the electrogenic sodium pump in guinea-pig atria by external potassium ions

1. When cardiac preparations are rewarmed following prolonged hypothermia a transient hyperpolarization occurs in K-containing media. This hyperpolarization is correlated with the active Na efflux. It might be due to electrogenic Na pumping or to extracellular K depletion brought about by the activity of an electroneutral Na-K exchange pump. In order to distinguish between these mechanisms the effect of various extracellular K concentrations ([K](o)) on the membrane potential of guineapig atria was studied before and after hypothermia.2. The membrane potential increased with decreasing [K](o) before cooling. It reached values of -64 and -92 mV at 10.8 and 0 mM-K, respectively.3. The membrane hyperpolarized transiently after hypothermia beyong the potential observed before cooling. Maximal values of about -94 mV were obtained during rewarming in solutions containing 0.4-2.7 mM-K. The membrane potential was significantly lower (-88 mV) in K-free media. It was also diminished at [K](o) higher than 2.7 mM and was measured to be -74 mV at 10.8 mM-K.4. The hyperpolarization of the cell membrane during the first 20 min of rewarming was maximal at 2.7 mM-K and yielded 15.5 mV. The hyperpolarization amounted to 7.2 and 10 mV at 0.4 and 10.8 mM-K, respectively. No hyperpolarization occurred in K-free solutions.5. The rate of decline of the transient hyperpolarization increased with [K](o).6. Variations of membrane input resistance after changes in [K](o) were measured in rewarmed atrial trabecula. The measurements revealed an increase in membrane resistance in lower [K](o).7. It is concluded that the transient hyperpolarization of the cardiac cell membrane during rewarming is due to the activation of an electrogenic Na pump.8. The (relative) strength of the pump current at various [K](o) was derived from the observed dependence of the hyperpolarization and of the membrane input resistance on [K](o). The current is estimated to be half-maximal at about 1.5 mM-K.