Biomedical subjects

Andrey K Tsaturyan

Publications and source records attributed to Andrey K Tsaturyan.

4 recordsLinked to original sources

PubMed2005

The "roll and lock" mechanism of force generation in muscle.

Muscle force results from the interaction of the globular heads of myosin-II with actin filaments. We studied the structure-function relationship in the myosin motor in contracting muscle fibers by using temperature jumps or length steps combined with time-resolved, low-angle X-ray diffraction. Both perturbations induced simultaneous changes in the active muscle force and in the extent of labeling of the actin helix by stereo-specifically bound myosin heads at a constant total number of attached heads. The generally accepted hypothesis assumes that muscle force is generated solely by tilting of the lever arm, or the light chain domain of the myosin head, about its catalytic domain firmly bound to actin. Data obtained suggest an additional force-generating step: the "roll and lock" transition of catalytic domains of non-stereo-specifically attached heads to a stereo-specifically bound state. A model based on this scheme is described to quantitatively explain the data.

Actins↗

PubMed2004

Strong binding of myosin heads stretches and twists the actin helix.

Calculation of the size of the power stroke of the myosin motor in contracting muscle requires knowledge of the compliance of the myofilaments. Current estimates of actin compliance vary significantly introducing uncertainty in the mechanical parameters of the motor. Using x-ray diffraction on small bundles of permeabilized fibers from rabbit muscle we show that strong binding of myosin heads changes directly the actin helix. The spacing of the 2.73-nm meridional x-ray reflection increased by 0.22% when relaxed fibers were put into low-tension rigor (<10 kN/m(2)) demonstrating that strongly bound myosin heads elongate the actin filaments even in the absence of external tension. The pitch of the 5.9-nm actin layer line increased by approximately 0.62% and that of the 5.1-nm layer line decreased by approximately 0.26%, suggesting that the elongation is accompanied by a decrease in its helical angle (approximately 166 degrees) by approximately 0.8 degrees. This effect explains the difference between actin compliance revealed from mechanical experiments with single fibers and from x-ray diffraction on whole muscles. Our measurement of actin compliance obtained by applying tension to fibers in rigor is consistent with the results of mechanical measurements.

Actins↗

PubMed2002

The elementary force generation process probed by temperature and length perturbations in muscle fibres from the rabbit.

Single chemically permeabilized fibres from rabbit psoas muscle were activated maximally at 5-6 degrees C and then exposed to a rapid temperature increase ('T-jump') up to 37 degrees C by passing a high-voltage pulse (40 kHz AC, 0.15 ms duration) through the fibre length. Fibre cooling after the T-jump was compensated by applying a warming (40 kHz AC, 200 ms) pulse. Tension and changes in sarcomere length induced by the T-jumps and by fast length step perturbations of the fibres were monitored. In some experiments sarcomere length feedback control was used. After T-jumps tension increased from approximately 55 kN m(-2) at 5-6 degrees C to approximately 270 kN m(-2) at 36-37 degrees C, while stiffness rose by approximately 15 %, suggesting that at a higher temperature the myosin head generates more force. The temperature-tension relation became less steep at temperatures above 25 degrees C, but was not saturated even at near-physiological temperature. Comparison of tension transients induced by the T-jump and length steps showed that they are different. The T-jump transients were several times slower than fast partial tension recovery following length steps at low and high temperature (phase 2). The kinetics of the tension rise after the T-jumps was independent of the preceding length changes. When the length steps were applied during the tension rise induced by the T-jump, the observed complex tension transient was simply the sum of two separate responses to the mechanical and temperature perturbations. This demonstrates the absence of interaction between these processes. The data suggest that tension transients induced by the T-jumps and length steps are caused by different processes in myosin cross-bridges.

Animals↗

PubMed2002

Diffraction by partially occupied helices.

An expression for cylindrically averaged intensity diffracted by a partially occupied helix (i.e. by a set of identical molecules bound to some, but not all, points of a discrete helix) is derived. The result is compared with previous studies and its application to muscle diffraction is discussed.

Actins↗