PubMed · 5497724
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I Wadsö. 1970. Microcalorimeters.. https://doi.org/10.1017/s0033583500004790
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Mutation of Saccharomyces cerevisiae leads to an alteration of the size and surface structure of the mutant cell. These phenomena are correlated with change in the lipid composition and hence membrane fluidity of the plasma membranes. Such alterations are in the fatty acyl constituents of phospholipids and glycolipids and include changes in the saturation or length of fatty acyl chains. Simultaneously, the "melting point" of phospholipid fractions, i.e. the temperature of the ordered-disordered phase transition and mixing behavior, changed. Consequently calorimetry on isolated phospholipid fractions extracted from plasma membranes is a useful analytical method to demonstrate directly such phase transitions and change in the mixing behavior of the cellular lipid fractions in connection with mutation. A correlation between the alteration of the lipid composition in the plasma membrane of strains of S. cerevisiae S 288 and its mutant VY 1160 is discussed.
BACKGROUND AND METHODS: Some obese subjects repeatedly fail to lose weight even though they report restricting their caloric intake to less than 1200 kcal per day. We studied two explanations for this apparent resistance to diet--low total energy expenditure and underreporting of caloric intake--in 224 consecutive obese subjects presenting for treatment. Group 1 consisted of nine women and one man with a history of diet resistance in whom we evaluated total energy expenditure and its main thermogenic components and actual energy intake for 14 days by indirect calorimetry and analysis of body composition. Group 2, subgroups of which served as controls in the various evaluations, consisted of 67 women and 13 men with no history of diet resistance. RESULTS: Total energy expenditure and resting metabolic rate in the subjects with diet resistance (group 1) were within 5 percent of the predicted values for body composition, and there was no significant difference between groups 1 and 2 in the thermic effects of food and exercise. Low energy expenditure was thus excluded as a mechanism of self-reported diet resistance. In contrast, the subjects in group 1 underreported their actual food intake by an average (+/- SD) of 47 +/- 16 percent and overreported their physical activity by 51 +/- 75 percent. Although the subjects in group 1 had no distinct psychopathologic characteristics, they perceived a genetic cause for their obesity, used thyroid medication at a high frequency, and described their eating behavior as relatively normal (all P < 0.05 as compared with group 2). CONCLUSIONS: The failure of some obese subjects to lose weight while eating a diet they report as low in calories is due to an energy intake substantially higher than reported and an overestimation of physical activity, not to an abnormality in thermogenesis.
Thermodynamic properties of a mutant lambda Cro repressor with Cys replacing Val55 were studied calorimetrically. Formation of the S-S cross-link between neighboring Cys55 residues in this dimeric molecule leads to stabilization of a structure formed by the C-terminal parts of the two polypeptide chains, which behave as a single cooperative domain upon protein denaturation by heating. This composite domain is very stable at neutral pH and disrupts at 110 degrees C. The S-S-cross-linked tryptic fragment (residues 22-66), which includes this C-terminal domain, has similar stability. The N-terminal parts of the polypeptide chains do not form any stable structure when isolated, but in S-S-cross-linked dimer, they form a single cooperative block which melts in an all-or-none way 9 degrees C higher than the un-cross-linked protein. The observed cooperation of the distant N-terminal parts in dimer raises questions regarding lambda Cro repressor structure in solution.