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Biomedical subjects

J M Sturtevant

Publications and source records attributed to J M Sturtevant.

At least 109 records · Page 6Linked to original sources
PubMed1981

Calorimetric study of the interaction of lysozyme with aqueous 1-propanol.

The enthalpies of transfer of hen egg white lysozyme from water to aqueous solutions of 1-propanol were determined by isothermal flow calorimetry at 10, 17, 25, and 40 degrees C in 0.04 M, pH 2 glycine buffer. Alcohol concentrations up to 3.4 M were employed. Four regions in the dependence of the enthalpy of transfer on alcohol concentration can be discerned: a region of linear increase observable at 10, 17, and 25 degrees C, an inflection region observed at 17 and 25 degrees C, a second linear region observable at 17, 25, and 40 degrees C, and a region of decreasing enthalpies seen at 40 degree C. Combination of differential scanning calorimetric data on lysozyme in PrOH-H2O mixtures [Velicelebi, G., & Sturtevant, J. M. (1979) Biochemistry 18, 1180-1186] with the transfer enthalpies reported here shows that the enthalpy in the system can be regarded as a state function and that the apparent specific heat is at first slightly decreased and then strongly increased by the addition of 1-propanol. Comparison of the results of the interaction with guanidine hydrochloride [Pfeil, W., & Privalov, P. L. (1976) Biophys. Chem. 4, 23-50] indicates that the denaturing effects of these two reagents involve very different mechanisms.

1-Propanol↗
PubMed1981

Thermotropic behavior of bilayers formed from mixed-chain phosphatidylcholines.

The six possible phosphatidylcholines containing two different chains derived from myristic, palmitic, and stearic acids were synthesized, and their bilayer structures were investigated by high-sensitivity differential scanning microcalorimetry. Chain migration during the syntheses caused each of the lipids to contain about 10% of the corresponding positional isomer. A phase diagram for each pair of isomers was constructed to permit estimation of the transition properties of the pure mixed-length phospholipids. The phase transitions of these lipids were found to be similar to those of saturated like-chain phosphatidylcholines. The main transition temperatures and enthalpies fall within the range of those for the like-chain lipids. In each pair of positional isomers, the isomer having the longer chain at position 2 on the glycerol backbone has the higher transition temperature and enthalpy. The transition curves of the pure mixed-chain lipids with myristic acid at position 2 and either palmitic or stearic acid at position 1 exhibited two partially separated peaks for the main transition. No satisfactory interpretation of this unexpected phenomenon has been developed.

Calorimetry, Differential Scanning↗
PubMed1981

Application of differential scanning microcalorimetry to the study of cellular processes: heat production and glucose oxidation of murine macrophages.

Differential scanning microcalorimetry provides a noninvasive method for studying heat evolution in living cells. We used this technique to measure the heat evolved by thioglycollate broth-elicited mouse macrophages, and the effects of NaF, KCN, cycloheximide, and cytochalasins B and D on this parameter. The total heat evolved in the interval 10--37 degrees C scanned at 1 degree C min-1 ranged from 300 to 2500 X 10(-12) cal (1 Cal = 4.184 J) per cell, depending on cell density, glucose concentration, and the presence or absence of various drugs.

Animals↗
PubMed1980

Stability of DNA in nucleosomes.

Heats of thermal denaturation of chromatin core particles and core particles with covalently crosslinked histones were measured by differential scanning calorimetry. The additional stabilization of the nucleoprotein complex by crosslinking is not reflected in the transition enthalpy. The contribution of protein denaturation to the total heat was estimated by comparison of core particles with core particle DNA in a high-salt solution. By taking into account the temperature dependence of the transition enthalpy of DNA, we conclude that the enthalpy change for denaturation of DNA in core particles is nearly the same as that for naked DNA in solution.

Calorimetry↗
PubMed1980

Observation of an exothermic process associated with the in vitro polymerization of brain tubulin.

The polymerization of tubulin has been studied with a high-sensitivity differential scanning microcalorimeter, with results which indicate that microtubule assembly can proceed via one or possibly two exothermic reactions. The amount of heat evolution has been found to be far in excess of GTP hydrolysis. The heat liberated has been observed to depend strongly upon the exact experimental conditions, varying from many hundreds of kilocalories per mole of tubulin dimer when dilute tubulin solutions are heated rapidly to a few kilocalories per mole of tubulin dimer when concentrated tubulin solutions are heated slowly. The results are tentatively interpreted in terms of the existence of at least two pathways for the formation of energetically distinct polymers. These findings indicate the importance of kinetic factors in studying tubulin polymerization.

Animals↗
PubMed1980

Scanning calorimetric evidence for a third phase transition in phosphatidylcholine bilayers.

A third phase transition, centered at about 18 degrees C, was observed by differential scanning calorimetry in a multilamellar suspension of dipalmitoyl phosphatidylcholine that had been held at 0 degrees C for several days. This transition is less cooperative than the other two transitions which are well known for this system, and it is accompanied by an enthalpy increase about three times as large as that of the so-called pretransition at 35 degrees C and about half that of the main gel to liquid crystal transition at 41 degrees C. The reversal of this transition on cooling is extremely slow.

Biophysical Phenomena↗
PubMed1979

Thermodynamics of the denaturation of lysozyme in alcohol--water mixtures.

The thermal denaturation of lysozyme was studied at pH 2 in aqueous mixtures of methanol, ethanol, and 1-propanol by high sensitivity differential scanning calorimetry (DSC). The most obvious effect of alcohols was the lowering of Td, the temperature of denaturation, increasingly with higher alcohol concentration and longer alkyl chain. Both the calorimetric and van't Hoff enthalpies of denaturation initially increased and then decreased with increasing alcohol concentration, the ratio of the two enthalpies being nearly unity, 1.007 +/- 0.011, indicating the validity of the two-state approximation for the unfolding of lysozyme in these solvent systems. The reversibility of the denaturation was demonstrated by the reversibility of the DSC curves and the complete recovery of enzymic activity on cooling. The changes in heat capacity on unfolding decreased with increasing alcohol concentration for each alcohol. Experimentally determined values of denaturation temperature and of entropy and heat capacity changes were used to derive the additional thermodynamic parameters delta G degrees and delta S degrees for denaturation as a function of temperature for each alcohol--water mixture. Comparison of the thermodynamic parameters with those reported [Pfeil, W., & Privalov, P.L. (1976) Biophys. Chem. 4, 23--50] in aqueous solution at various values of pH and guanidine hydrochloride concentration showed that these latter changes have no effect on the heat capacity changes, whereas the addition of alcohols causes a sharp decrease.

Alcohols↗
PubMed1979

The lambda repressor contains two domains.

Papain digestion of the lambda phage repressor produces two fragments that are relatively resistant to further digestion. One includes the amino terminus (residues 1-92) and the other the carboxyl terminus (residues 132-236). Calorimetry shows that the amino-terminal fragment denatures near 50 degrees C and that the carboxyl-terminal fragment denatures near 70 degrees C. Intact repressor undergoes two denaturations, one near 50 degrees C and another near 70 degrees C. These and other data show that lambda repressor consists of two domains joined by a "connector" 40 amino acids long that is sensitive to proteases. The amino-terminal domain binds DNA, and the carboxyl-terminal domain oligomerizes.

Amino Acid Sequence↗
PubMed1979

Thermotropic behavior of some fluorodimyristoylphosphatidylcholines.

The thermotropic behavior of three fluorinated phospholipids has been studied by means of high-sensitivity differential scanning calorimetry. The three lipids are 1,2-di(X,X-difluoromyristovyl)phosphatidylcholine with X = 4,8, or 12. The compound with X = 4 has a higher transition temperature than dimyristoylphosphatidylcholine whereas the other two have lower values. All three lipids have transition enthalpies approximately twice that of the unsubstituted lipid. It was found the substituted lipids form strikingly nonideal mixtures with the parent compound. In view of these observations it is evident that results obtained using these or related compounds as probes of bilayer or membrane behavior must be interpreted with due caution. Some of the properties exhibited by geminal fluorine atoms in fluorinated phospholipids appear to be similar to those of cis double bonds in lipids.

Calorimetry↗
PubMed1978

Phase behavior of lipids from Halobacterium halobium.

Mixtures of dipalmitoylphosphatidylcholine with purple membrane lipids, red membrane lipids, or total lipids of Halobacterium halobium have been studied with differential scanning calorimetry. A comparison of red and purple membrane lipids reveals no difference in their phase behavior, indicating that lipid phase behavior plays no role in the in vivo separation of red and purple membranes. The effects of variation of the salt content of the suspending solution have also been examined. Studies of the melting behavior of these mixtures as H. halobium lipid content is varied suggest that the gel to liquid-crystal transition does not occur in the lipids of H. halobium.

Bacteriorhodopsins↗
PubMed1978

High-sensitivity scanning calorimetric study of mixtures of cholesterol with dimyristoyl- and dipalmitoylphosphatidylcholines.

A highly sensitive and stable scanning microcalorimeter is employed in a reinvestigation of the effect of cholesterol on multilamellar suspensions of dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC). Below 20 mol % cholesterol the DPPC mixtures give heat-capacity curves each of which can be resolved into a narrow and a broad peak, suggesting the coexistence of two immiscible solid phases; above 20 mol % only the broad peak is observed and this disappears at about 50 mol %. The DMPC mixtures show a more complicated behavior; from about 13.5 to 20 mol % cholesterol the observed curves appear to be the sum of three component peaks. As with the DPPC mixtures, only a single broad peak is observed above 20 mol % cholesterol, and this broad peak becomes undetectable above about 50 mol %. These results are discussed.

Calorimetry, Differential Scanning↗
PubMed1978

Phase transitions of the purple membranes of Halobacterium halobium.

Purple membranes of Halobacterium halobium were studied by differential scanning calorimetry. No transition was detected at temperatures below 70 degrees C. A small endothermic transition was seen at about 80 degrees C and a larger one at 100 degrees C. The larger transition is the irreversible denaturation of bacteriorhodopsin. The smaller transition is accompanied by a change in the visible absorption spectrum and is believed to be reversible, involving a cooperative change in crystalline structure of the membrane.

Bacteriorhodopsins↗
PubMed1978

Nature of the gel to liquid crystal transition of synthetic phosphatidylcholines.

High sensitivity differential scanning calorimetry is employed in the study of the gel to liquid crystal phase transition of a highly purified sample of dipalmitoylphosphatidylcholine in multilamellar bilayer suspension. It is concluded from the calorimetric data that the purity of the sample is better than 99.94 mol % and that the transition closely approximates an isothermal first-order transition.

Calorimetry↗
PubMed1978

Proposed temperature-dependent conformational transition in D-amino acid oxidase: a differential scanning microcalorimetric study.

A number of authors have reported observations on D-amino acid oxidase [D-amino acid: O2 oxidoreductase (deaminating), EC 1.4.3.3.] that they have interpreted in terms of a temperature-dependent conformational transition having a van't Hoff enthalpy amounting to more than 1 cal per g of protein (1 cal = 4.184J). No indication of this transition is obtained by using a differential scanning calorimeter having a sensitivity considerably in excess of that required to detect such a transition. The implications of this discrepancy are discussed.

Apoenzymes↗
PubMed1977

Studies of the lipid phase transitions of Escherichia coli by high sensitivity differential scanning calorimetry.

High sensitivity adiabatic differential scanning calorimetry was performed on lipids, membrane vesicles, and whole cells of Escherichia coli enriched in particular unsaturated fatty acids by genetic means. Information concerning the shape of the transition is discussed. Transitions with an asymmetric shape reminiscient of a second order transition were observed. Comparison between the lipid transition observed in whole cells, membrane vesicles, and extracted lipids enriched in elaidate reveal some basic similarities. Studies of synthetic lipids were undertaken in an attempt to interpret the shapes of these transitions as a function of the lipid components of the membrane.

Calorimetry↗
PubMed1977

A calorimetric examination of stable and fusing lipid bilayer vesicles.

Mixed lipid samples containing dimyristoylglycerophosphocholine and small amounts of myristic acid were examined calorimetrically. Examination of multilamellar and small vesicle samples indicated that upon heating small vesicles combine to form more extended structures. An exothermic peak (at 19 . 5 degrees C) can be associated with the structural transformation. The enthalpy for this process, which may be interpreted as vesicle-vesicle fusion, is found to be approx.--2 kcal/mol.

Calorimetry↗