Corresponding changes in kynurenine hydroxylase activity, membrane fluidity, and sterol composition in Saccharomyces cerevisiae mitochondria

Abstract

The effect of sterol composition on the properties of the mitochondrial membrane of Saccharomyces cerevisiae was investigated. The physical state of mitochondrial membranes from wild-type strains and sterol mutants was compared, using a fluorescence polarization technique with 1,6-diphenyl-1,3,5-hexatriene. Changes in the rate of depolarization of the probe molecule as a function of temperature suggest the occurrence of a phase transition in the mitochondrial membranes isolated from the sterol mutants but not in the membranes isolated from the wild types. Arrhenius kinetics of the mitochondrial membrane-bound enzyme L-kynurenine-3-hydroxylase exhibited changes in activation energy at temperatures similar to those observed in the fluorescence polarization study. The ratio of mitochondrial sterol to phospholipid and the phospholipid fatty acid composition of the organisms were characterized.

Effect of altered sterol composition on the osmotic behavior of sphaeroplasts and mitochondria ofSaccharomyces cerevisiae

“…The strains of S. cerevisiae and their sterol phenotypes used in this study are summarized in Table 1. These strains and the defects in sterol biosynthesis have been characterized in previous communications (1,4).…”

“…Sphaeroplasts were prepared by treatment with snail gut enzyme (1) or an extracellular lyticase from Oerskovia xanthineolytica (5). The lyticase was prepared by dialysis of the medium following growth of O. xanthineolytica on modified Sistrom's medium (5) against buffer containing 1.1 M sorbitol, 10 mM phosphate and 1 mM EDTA, pH 7.4.…”

“…Following digestion, the sphaeroplasts were washed three times and suspended in 1.1 M sorbitol, 10 mM phosphate and 1 mM EDTA, pH 7.4, in the case of FY3-n3 or in 0.7 M sorbitol, 0.3 M mannitol, 0.1 M citric acid, 0.01 M potassium phosphate and 10 mM EDTA, pH 7.4, for all other preparations. Mitochondria were isolated in buffer containing 0.9 M sorbitol, 0.5 mM EDTA and 10 mM Tris, pH 7.4, as described by McLean-Bowen and Parks (1).…”

“…A recent report from our laboratory examined the physical state of mitochondrial membranes from wild-types and from mutants defective in ergosterol biosynthesis using a fluorescence polarization technique (1). Changes in the depolarization rate of the probe molecule as a function of temperature indicated the occurrence of a phase transition in the mitochondrial membranes isolated from mutants but not seen in mitochondria isolated from wild-types.…”

Induction of petite yeast mutants by membrane-active agents

“…In organelles, such as mitochondria, in which membranes control the function of the organelle, it is essential to know how the sterol is distributed; Bottema and Parks (6) have found that the sterol-to-phospholipid molar ratio was very similar between the inner and outer membranes of yeast mitochondria. Additionally, the types of sterols present affect the physical properties of the mitochondrial membrane so that qualitative changes in the sterol components produce a wide range of fluidities (2,3,17,22).…”