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Biomedical subjects

L A Blumenfeld

Publications and source records attributed to L A Blumenfeld.

15 recordsLinked to original sources
PubMed2000

Cervimetry: a review of methods for measuring cervical dilatation during labor.

Several different methods of measuring cervical dilatation have been described. In this article, we review those methods and examine findings from studies using them. Although many instruments have been developed to measure cervical dilatation during labor and their use as a research tool has been established, no device has yet been successfully used for clinical obstetrics. The ideal device has not yet been developed; however, because repeated digital cervical examinations are time consuming for the clinician, are poorly reproducible, and are uncomfortable for the patient, continued efforts to develop a cervimeter suitable for clinical use is a worthwhile endeavor.

Cervix Uteri↗
PubMed1988

Physical mechanism of ATP formation in biomembranes.

Membrane-bound and isolated H+ ATPases of various origin are able to synthesize ATP from ADP and Pi after a jump-like pH increase. In the course of this increase the pH of solution (or suspension) must cross a value corresponding to pK of certain acid groups in the catalytic component of ATPase. In the case of isolated soluble enzymes it is possible to obtain up to 10 ATP molecules per one pH jump per one enzyme molecule. A physical mechanism of this phenomenon as well as of oxidative and photosynthetic phosphorylation is suggested.

Adenosine Diphosphate↗
PubMed1986

A model of the mechanism of enzyme action in terms of protein conformational relaxation.

A theoretical model of enzymatic reaction is formulated in which the modulation of the reaction coordinates by low-frequency conformational motions of the enzyme molecule causes the lowering of the activation energy barriers until they completely disappear. If the rates of electron transitions in the enzyme-substrate complex exceed the characteristic frequencies of conformational motions then the rate of the elementary enzymatic reaction shows hysteresis dependence on temperature and substrate concentration.

Catalysis↗
PubMed1982

PH-jump-induced ADP phosphorylation in mitochondria.

Mitochondria, uncoupled by aging or by freeze-thaw treatment, are able to synthesize ATP from ADP and Pi after a fast increase (but not decrease) in the external pH. The maximal ATP yield (approx. 2.5 ATP molecules/electron-transport chain per pH jump) can be obtained under the following conditions: (1) the pH change during the jump must exceed 0.7 pH units; (2) in the course of this change, the pH of the mitochondrial suspension must cross the pH 8.1-8.3 value. This pH-jump-induced ATP synthesis is completely inhibited by oligomycin.

Adenosine Diphosphate↗
PubMed1979

Spectral properties of nonequilibrium states in cytochrome P-450 formed by reduction at subzero temperatures.

Nonequilibrium conformational states in cytochrome P-450 in the presence and absence of substrates formed by reduction at subzero temperatures with hydrates electrons were obtained and characterized by their absorption spectra. Different absorption spectra between the relaxed (298 K) and the non-relaxed enzyme forms (77 K) indicate conformational changes proceeding in the relaxed form after reduction of the heme iron which lead to altered interactions between the active centre and its environment in the protein. The two maxima of the nonequilibrium form of cytochrome P-450 without substrate in the visible absorption spectrum (alpha-band, beta-band) and the ratio of their intensities indicate the low-spin character of the heme iron. These spectral properties give evidence for a reduced cytochrome P-450 with two heme-linked axial ligands.

Animals↗
PubMed1977

The chemical properties of out-of-equilibrium states of proteins and the role of these states in protein functioning.

The out-of-equilibrium states of several iron-containing proteins (cytochromes c of different origin, haemoglobin, myoglobin, ferredoxin and other non-haem iron proteins, cytochrome c oxidase, horseradish peroxidase) were recorded after fast changes in the active centre (electron reduction of iron, ligand dissociation). Strained states result in which the active centre has already been changed and undergone vibrational relaxation but the main part of protein globule is in the 'old', now out-of-equilibrium, state. Protein structure and chemical properties in these states differ considerably from those in equilibrium states. As a rule, the rate constants of protein-specific chemical reactions increase in out-of-equilibrium states by 1--3 orders of magnitude in comparison with those in equilibrium states. Spectra and reactivity of these proteins change in the course of slow (up to 10(-1) s) conformational relaxation, continuously approaching the equilibrium values. It seems that this conformational relaxation is essentially the elementary act of many enzymic reactions for which the rate of substrate-product transformation is determined by the rate of this conformational change.

Cytochrome c Group↗
PubMed1975

Studies on the conformational changes of metalloproteins induced by electrons in water-ethylene glycol solutions at low temperatures. III. Adrenal ferredoxin.

The reduction of adrenal ferredoxin (adrenodoxin) at low temperatures was investigated in order to separate local modifications of the active centre of the protein on its reduction, from the conformational transition which seems to accompany the change of the redox state of the irons; The ESR spectra of the states of the protein, where the reduced active centre is to be found by the "oxidized" conformation of the apoprotein, were obtained. The transition from the states of the protein to the state which occurs on its chemical reduction at room temperature was also investigated. The results of the work support the view that conformational changes in proteins (enzymes) which take place while they are functioning proceed after modifications of the active centres (change of the redox state, adsorption of a substrate, etc.), and are essentially caused by them. Adrenal ferredoxin was the third subject in our studies of the intermediate states of proteins which appear after reduction of their active centres by means of electrons trapped in water-ethylene glycol mixtures at the temperature of liquid nitrogen [1, 2]. In the reduced state, the active centre of the protein has an ESR signal with a g-factor of 1.94 [3, 4] which is convenient for our purposes.

Adrenodoxin↗