[Calorimetric study of stable complexes of myosin subfragment I with adenosine diphosphate and phosphate analogs]. / Kalorimetricheskie issledovaniia stabil'nykh kompleksov subfragmenta 1 miozina s analogami adenozindifosfata i fosfata.

This short review is concerned with the application of the method of differential scanning calorimetry to study the conformational changes of isolated myosin head (myosin subfragment 1, S1) caused by the formation of the S1 complexes with Mg(2+)-ADP and P(i) analogues such as orthovanadate (V), aluminium fluoride (AIF4-) or beryllium fluoride (BeFx). These changes of the whole S1 molecule are reflected in a significant increase of S1 thermal stability and in a pronounced increase of the cooperativity of the thermal denaturation. Since the complexes S1-ADP-V, S1-ADP-AIF4- and S1-ADP-BeFx are stable analogues of the S1**-ADP-P(i) transition state of the S1-catalyzed ATP hydrolysis, it is concluded that DSC studies with these complexes offer a new and promising approach to investigate the structural changes which occur in the myosin head during Mg(2+)-ATPase reaction.

[Interaction of isoforms of subfragment-1 of myosin, containing fluorescently labelled alkaline light chains, with muscle fiber actin]. / Vzaimodeistvie izoform subfragmenta-1 miozina, soderzhashchikh fluorestsentno mechennye shchelochnye legkie tsepi, s aktinom myshechnykh volokon.

Using polarization microfluorimetry, the interaction of myosin subfragment 1 (S1) isoforms containing alkali light chains A1 and A2 respectively (S1(A1) and S1(A2] with F-actin of single glycerinated rabbit skeletal muscle fibers was studied. The alkali light chains of S1 were substituted by reassociation for A1 or A2 chains modified by a fluorescent label (1.5-IAEDANS) at the single SH-group located in the C-terminus. It was found that in S1(A1) bound to muscle fiber F-actin the mobility of the fluorescent label is lower than in S1(A2). At the same time the S1(A1) and S1(A2) interaction with F-actin induces similar changes in polarized fluorescence of rhodamine linked to falloidine which, in turn, is specifically bound to F-actin. It is concluded that the both S1 isoforms bind to F-actin and produce similar effects on the conformational state of actin filaments in muscle fibers. Local differences between S1(A1) and S1(A2) seem to be due to the interaction of the N-terminus of A1 within S1(A1) with the C-terminal region of actin.

[Effect of myosin alkali light chains on myosin subfragment 1 interaction with actin in solution and in ghost muscle fiber]. / Vliianie shchelochnykh legkikh tsepei miozina na vzaimodeistvie subfragmenta 1 miozina s aktinom v rastvore i v tenevom myshechnom volokne.

At low ionic strength (7-25 mM) Mg2(+)-ATPase of myosin subfragment 1 (S1) isoforms containing alkali light chain A1 [S1(A1)] is activated by actin 1.5-2.5 times as strongly as Mg2(+)-ATPase of S1 isoforms containing alkali light chain A2[S1(A2)]. Data from analytical ultracentrifugation suggest that at low ionic strength in the absence of ATP in solution S1(A1) displays a higher affinity for F-actin than S1(A2). Such a higher affinity of S1(A1) for F-actin was also demonstrated by experiments, in which the interaction of S1 isoforms fluorescently labeled by 1.5-IAEDANS with F-actin of ghost fibers (single glycerinated muscle fibers containing F-actin but devoid of myosin) was studied. Using polarization microfluorimetry, it was shown that the interaction of both S1 isoforms with ghost fiber F-actin induces similar changes in the parameters of polarized tryptophan fluorescence. At the same time the mobility of the fluorescent probe, 1.5-IAEDANS, specifically attached to the SH-group of Cys-374 in the C-terminal region of action is markedly decreased by S1(A1) and is only slightly affected by S1(A2). The data obtained suggest that S1(A1) and S1(A2) interact with the C-terminal region of the actin molecule in different ways, i.e. S1(A1) is attached more firmly than S1(A2). This may be due to the existence of contacts between the alkali light chain of A1 of S1(A1) and the C-terminal region of actin as well as to the absence of such contacts in the case of S1(A2).

[Study of thermal denaturation of the rod part of myosin molecule by microcalorimetry and intrinsic fluorescence methods]. / Issledovanie teplovoi denaturatsii sterzhnevoi chasti molekuly miozina metodami mikrokalorimetrii i sobstvennoi fluorestsentsii.

Thermal denaturation of myosin rod has been studied by differential scanning microcalorimetry and intrinsic tryptophane fluorescence methods. Use of the sequence annealing in the calorimetric measurement allows to decompose the total thermogram of rod into four elementary bands with maxima at 42, 46.5, 50 and 57 degrees C. Fluorescence changes occur at temperatures which coincide with the first, second and fourth calorimetric peaks. Changes of the time resolved and steady state fluorescence of myosin rod were interpreted using the data on localization of tryptophan residues in the molecule. The tryptophan fluorescence of myosin rod is assumed to monitor the denaturational changes in high meromyosin and probably in the hinge region but not in the subfragment 2.

[Isolation of biologically active halves of the long tail fibers and whiskers of bacteriophage T4]. / Vydelenie biologicheski aktivnykh polovinok dlinnykh khvostovykh fibrill i bakenbard bakteriofaga T4.

The following substructural elements of bacteriophage T4 have been isolated in homogeneous and biologically active state: the whole long tail fibrils, distal and proximal halves of the long tail fibrils and whiskers. It has been shown that during the infection of Escherichia coli with T4 amber-mutants (defective in the genes coding for heads and tails), the major part of distal and proximal fibril halves found within the cell appears to be unassociated. The interaction of distal and proximal fibril halves with the bacteriophage particle is necessary for the whole tail fibril formation to proceed effectively.