Structural and conformational changes in myocardial and erythrocyte actin during cardiac ischemia.

Structural and conformational changes in myocardial and erythrocyte actin during cardiac ischemia were studied by the method of fluorescence resonance energy transfer with highly selective fluorescent probes. In contrast to 15-min coronary artery occlusion, 120-min ischemia was accompanied by irreversible structural and conformational changes in the small domain of erythrocyte actin. Posttranslational changes during myocardial ischemia concerned the N- and C-terminal regions of actin and went beyond the allowed conformational fluctuations in the actin molecule without breaking the energy barrier. Our results suggest that under conditions of ischemia, actin of the myocardium and erythrocyte cytoskeleton loses its ability to acquire conformation required for force generation by cardiomyocyte myofibrils and maintenance of elasticity and integrity of the erythrocyte membrane.

Subcellular and molecular mechanisms of the effects of cardiac glycosides and angiotensin-converting enzyme inhibitors on contractile function and energy conversion in myocardial myofibrils under normal conditions and during acute cardiac insufficiency.

Experiments on skinned and hybrid myocardial fibers isolated from normal dogs and animals subjected to 120-min occlusion of the anterior interventricular branch of the coronary artery showed that in contrast to cardiac glycosides, angiotensin-converting enzyme inhibitors suppress contractile ability of myocardial myofibrils in a dose-independent manner within the concentration range of 10(-12)-10(-4)M. This effect is accompanied by a decrease in fiber relaxation rate most pronounced in the presence of captopril. Actin, the major protein of fine filaments is the target for b-acetyldigoxin, K-strophanthin, captopril, enalapril, and trandolapril in myocardial myofibrils. During coronary occlusion, the inhibitors of angiotensin-converting enzyme induce structural and conformational changes in actin that decrease efficiency of contraction. The data obtained cast doubt on advisability of therapeutic use of angiotensin-converting enzyme inhibitors in the therapy of myocardial infarction, especially in its early period.

Electron microscopy of the complexes of ribulose-1,5-bisphosphate carboxylase (Rubisco) and Rubisco subunit-binding protein from pea leaves.

The structure of ribulose-1,5-bisphosphate carboxylase (Rubisco) subunit-binding protein and its interaction with pea leaf chloroplast Rubisco were studied by electron microscopy and image analysis. Electron-microscopic evidence for the association of Rubisco subunit-binding protein, consisting of 14 subunits arranged with 72 point group symmetry, and oligomeric (L8S8) Rubisco was obtained.

[Various parameters of the structure of F-actin filaments of the normal and athyreotic myocardium]. / Nekotorye parametry struktury nitei F-aktina miokarda normal'nogo i atireoznogo serdtsa.

A comparative analysis of optical diffraction of electron micrographs of F-actin from normal and athyreosic myocardia showed abrupt changes of relative intensities of the reflexes nearest to the meridian in the athyreosic actin pattern. It indicates that under athyreosis changes in the actin globules or in their location in the fibril take place.

[Electron microscopy of glutamine synthetase from pea leaf chloroplasts]. / Elektronnaia mikroskopiia glutaminsintetazy iz khloroplastov list'ev gorokha.

Using electron microscopy, the spatial structure of glutamine synthetase from pea leaf chloroplasts was studied. The enzyme was shown to consist of eight elongated subunits, which are arranged with a point of 42 symmetry at the vertices of two squares. These squares are twisted about a 4-fold axis at 40 degrees relative to each other.

Electron microscopy of glutamine synthetase from pea leaf chloroplasts.

The structure of pea leaf chloroplast glutamine synthetase was studied by electron microscopy. The enzyme is shown to consist of eight elongated subunits which are arranged with point 42 symmetry at the vertices of two squares. These squares are twisted about the 4-fold axis at 40 degrees relative to each other.

Electron microscope study on human ceruloplasmin.

Electron microscopy of human ceruloplasmin (CP) molecules revealed a few distinctive types of particle images. Analysis of these images allows to propose a tentative model for CP: six "subunits" (which we call domains) not much different in size are arranged with 32 point group pseudosymmetry. The determination of the number of polypeptides arising at the spontaneous specific proteolytic fragmentation of CP and their molecular weights conform with this assumption. The electrophoretic studies of the CP samples prepared both with and without potent proteolytic inhibitor, PMSF, revealed that CP is a single-chain protein with molecular weight of 130 000. Isolated and stored without PMSF the polypeptide chain of CP undergoes specific proteolytic cleavage which results in the appearance of polypeptides with molecular weights of 16 000, 48 000, and 64 000. The latter two polypeptides degradate to about two- and three-fold decreased molecular weights fragments, respectively. Therefore, the single polypeptide chain of CP contains at least five peptide bonds which are particularly susceptible to proteolytic attack and which connect six principal segments of the chain. The hydrolysis of these bonds results in liberation of the six fragments which were integrated in the enzymatically active globule of CP.

[Quaternary structure of histidine decarboxylase according to small-angle x-ray diffraction and electron microscopic findings]. / Chetvertichnaia struktura gistidindekarboksilazy po dannym rentgenovskogo malouglovogo rasseianiia i élektronnoi mikroskopii.

The data on small angle X-ray scattering with histidine decarboxilase (HDC) from Micrococcus sp. n. were analysed and a line of succesively improving approximations of the molecule shape was found: by oblate ellipsoid a:b:c = 1:10.63, by continuous cylinder and hollow cylinder with H = 50 A, 2R = 76 A, 2r = 8A. Biochemical data and electron micrographs of HDC obtained made possible to distinguish subunits and thus to increase resolution of the model. The model of the enzyme molecule consisting of three subunits is suggested, whose X-ray small angle scattering curve well agrees with the experimental one up to value S = 0.21 A-1.

[Purification, properties and quaternary structure of glutamine synthetase from Chlorella]. / Ochistka, svoistva i chetvertichnaia struktura glutaminsintetazy Khlorelly

A highly purified preparation of glutamine synthetase from chlorella grown on a medium containing nitrate as a sole source of nitrogen, was isolated and characterized by disc-electrophoresis and analytical ultracentrifugation. The N-terminal amino acid of glutamine synthetase is glycine. The molecular weight of glutamine synthetase is 32.000; its activity in the presence of Mg2+ was 150 mkmol o-phosphate per min per mg protein. The molecular weight of subunits of the enzyme, equal to 53.000 was determined by disc-electrophoresis in polyacrylamide gel in the presence of sodium dodecyl sulfate. Electron microscopy of negatively contrasted enzyme preparations revealed 6 subunits in the enzyme molecule, arranged in a point symmetry group 32.