Non electrogenic function of the mitochondrial, alternative, cyanide-insensitive respiration in the yeast Saccharomycopsis lipolytica

Respiratory pathways in Hansenula saturnus

Hansenula saturnus is a petite-negative yeast species which displays a different pattern of respiration depending on the age of the cultures. The respiration is sensitive to antimycin A (AA) in the early exponential phase, is sensitive to the simultaneous addition of AA and salicylhydroxamic acid (SHAM) in the middle exponential phase and is sensitive to SHAM in the late exponential and stationary phase. The three respiratory activities are all associated to the mitochondrial fraction. The presence of AA in the growth medium determines the induction of the AA + SHAM-insensitive respiration which is 50% inhibited by 5 mM azide. On the contrary, the presence of erythromycin in the growth medium, which inhibits mitochondrial protein synthesis in this yeast species and the synthesis of cytochromes aa3 and b, totally prevents the appearance of AA + SHAM-insensitive respiration. Moreover, the antibiotic affects cell viability, suggesting a role of the mitochondrial protein synthesis in the cell cycle of H. saturnus.

Electrogenic proton ejection coupled to electron transport through the energy-conserving site 2 and K+/H+ exchange in yeast mitochondria

The proton ejection coupled to electron flow from succinate and/or endogenous substrate(s) to cytochrome c using the impermeable electron acceptor ferricyanide is studied in tightly coupled mitochondria isolated from two strains of the yeast Saccharomyces cerevisiae. (1) The observed H+ ejection/2e- ratio approaches an average value of 3 when K+ (in the presence of valinomycin) is used as charge-compensating cation. (2) In the presence of the proton-conducting agent carbonyl cyanide m-chlorophenylhydrazone, an H+ ejection/2e- ratio of 2 is observed. (3) The low stoichiometry of 3H+ ejected (instead of 4) per 2e- and the high rate of H+ back-decay (0.1615 ln delta (ngatom)H+/s and a half-time of 4.6 s for 10 mg protein) into the mitochondrial matrix are related to the presence of an electroneutral K+/H+ antiporter which is demonstrated by passive swelling experiments in isotonic potassium acetate medium.

Effect of chloramphenicol, antimycin A and hydroxamate on the morphogenetic development of the dimorphic ascomycete Endomycopsis capsularis

Mitochondrial protein synthesis, primary (antimycin-sensitive) respiration and secondary (antimycin-insensitive, salicyl-hydroxamate-sensitive) respiration, have been characterized in the dimorphic yeast Endomycopsis capsularis. The inhibition by chloramphenicol (CAP) of the morphogenetic development from the yeast-like form to the mycelial structure in this yeast could represent the intervention in the morphogenetic process of mitochondrial protein synthesis, since chloramphenicol blocks in vivo and in vitro mitochondrial protein synthesis. In fact, other functions such as primary and secondary respiration, do not seem to play a role in the morphogenetic development since their inhibition by antimycin A (AA) or by salicyl-hydroxamic acid (SHAM) does not affect the process. In addition, mitochondrial protein synthesis has been shown to be uninhibited by the two respiratory inhibitors.