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Membrane lateral pressure as a modulator of glycerol-3-phosphate dehydrogenase activity

Michaelis‐Menten kinetics of glycerol‐3‐phosphate dehydrogenase activity in proteoliposomes from brown adipose tissue mitochondria with exogenously added phospholipids or cholesterol was measured. It was shown that changes in membrane lipid composition affected the membrane lateral pressure and therefore modulated the enzyme activity, namely V max value. Contrarily, changes in surface charge caused by minute amounts of phosphatidylserine or charged organic substances influenced only the apparent K m value. The role of bulk phospholipids in regulation of glycerol‐3‐phosphate dehydrogenase is discussed.

Regulation of glycerol 3-phosphate oxidation in mitochondria by changes in membrane microviscosity

The inhibition of glycerol 3‐phosphate oxidation by oleic acid correlates with changes in membrane microviscosity monitored by the steady‐state fluorescence anisotropy of DPH. The dynamic measurements indicate that the changes of both the limiting anisotropy and rotational relaxation time occur in a concentration range where the enzyme activity is strongly inhibited.

Influence of thyroid status on the membranes of rat liver mitochondria Unique localization of L-glycerol-3-phosphate dehydrogenase

The effect of thyroid status on the physical properties of rat liver mitochondrial membranes and on the lipid microenvironment of proteins was investigated. The steady‐state fluorescence anisotropy of diphenyl‐1,3,5‐triene and 1‐[4‐{trimethylaminophenyl} phenyl]‐6‐phenylhexa‐1,3,5‐triene revealed an increase of the order of the membranes with the increase of hormone level. Protein arrangement in the inner mitochondrial membrane altered with the thyroid status, which was reflected by digitonin subfractionation of mitochondria. The microenvironment of FAD‐linked L‐glycerol‐3‐phosphate dehydrogenase was dramatically influenced by thyroxine.

The isolated H4‐H5 cytoplasmic loop of Na,K‐ATPase overexpressed in Escherichia coli retains its ability to bind ATP

The H4‐H5 loop of the α‐subunit of mouse brain Na,K‐ATPase was expressed and isolated from Escherichia coli cells. Using fluorescence analogues of ATP, this loop was shown to retain its capability to bind ATP. Isolation of a soluble H4‐H5 loop with the native ATP binding site is a crucial step for detailed studies of the molecular mechanism of ATP binding and utilisation.

Possible nystatin-protein interaction in yeast plasma membrane vesicles in the presence of ergosterol. A Förster energy transfer study

The Förster energy transfer from tryptophan residues of membrane proteins to nystatin was measured in reconstituted yeast plasma membrane vesicles free of, or doped with, ergosterol. We wanted to elucidate whether the functional change of membrane transport proteins from H+ symporters to facilitators, observed in ergosterol‐containing plasma membrane vesicles on addition of nystatin [Opekarová and Tanner (1994) FEBS Lett. 350, 46–50], is reflected in altered protein‐nystatin relations within the membrane. Both frequency‐domain and time‐domain time‐resolved fluorescence spectroscopy showed that in the presence of ergosterol nystatin is located much closer to membrane proteins than in its absence.

Effect of triadimefon on lipids, sterols, and membrane fluidity in submerged cultures of claviceps purpurea

Abstract Triadimefon (TDF) (5 mg · liter−1) stimulated the functions of chanoclavine cyclase in submerged cultures of high producing mutant Claviceps purpurea 59 with partially blocked oxidation and cyclization of chanoclavine. The culture growth decreased and specific clavine production was raised. The effect of TDF on growth and production was reversed by plant oil (7.2 g · liter−1), but not by ergosterol (10 mg · liter−1). The oil stimulated growth and lowered both specific alkaloid production and chanoclavin cyclase function. Ergosterol showed the opposite effects. TDF reduced the total mycelial lipids to 66%, sterols to 40%, and phospholipids to 72%. In the cultures supplemented with ergosterol, the sterol content increased 16-fold and phospholipids were lowered to 27%; however, the total lipid content remained unchanged. Oil increased all lipid components. The sterol content was indirectly proportional to the PC PE ratio in all cultures. The membrane fluidity of protoplasts from TDF-treated cultures was higher, in ergosterol-treated cultures lower, and unchanged in the presence of oil. The content of methylated sterols in the TDF-treated cultures was only 2% higher than in controls. The demethylation of sterols in Claviceps occurs first in position C-14, then in C-4. The chanoclavine cyclase function probably does not depend on membrane fluidity, but a correlation between higher activity and low phospholipid content was found.

Changes in Na+,K+‐ATPase structure induced by cation binding Approach by Raman spectroscopy

Raman analysis of Na+, K+‐ATPase structural changes induced by cation binding reveals a slight decrease (< 10%) of the α‐helical content upon E1–E2 transition. Pronounced conformational changes of the enzyme are unlikely as the character of the environment of tyrosine residues remains unaltered. However, local changes can take place as evidenced by changes in tryptophan vibration at about 880 cm−1.

Regulation of Lipid and Ergot Alkaloid Biosynthesis in Claviceps purpurea by Chlorophenoxy Acids

Summary Lipids influence ergot alkaloid biosynthesis in Claviceps purpurea mainly as structural elements of membranes. Chlorophenoxy acids (CPA) were applied to C. purpurea cultures to modify cellular lipid composition. Mutant strain C. purpurea 59 accumulating tricyclic clavines and two parental strains 35 and 129 were used. All the CPA - clofibrate, 2-(4-chlorophenoxy)-acetate and 2-(4-chlorophenoxy)-propionate (CPP) lowered lipid content. Fatty acid (FA) unsaturation index increased indicating a stimulation of FA-desaturation and also FA-elongation. Sterol biosynthesis was impaired mainly in the C(4)- and C(14)-demethylation resulting in a decrease of “membrane functional” (quasiplanar) sterols. Relative content of phosphatidylethanolamine decreased 1 Of old. Changes in lipids correlated with the decrease of microviscosity of cell membranes (measured as a steady state fluorescence anisotropy of the protoplast membranes with DPH and TMA-DPH as probes). CPP in subtoxic doses stimulated alkaloid production and changed alkaloid composition in the C. purpurea 59 strain impaired in chanoclavine cyclase function.