# MOLECULAR ANGLE TRANSITIONS IN MUSCLE

> **NIH NIH R01** · MAYO CLINIC ROCHESTER · 1993 · $165,113

## Abstract

The generation of force to produce muscle shortening takes place during
the hydrolysis of ATP in a muscle fiber.  The mechanism of converting the
chemical energy liberated from ATP hydrolysis into mechanical work
(energy transduction) involves structural changes in the myosin
cross-bridge.  The nature of these changes and how they make muscle work
is the central question in muscle research.  The purpose of the proposed
experiments is to elucidate the mechanism of the actomyosin interaction
and how it pertains to muscle shortening by determining the relative
movements of myosin and actin during contraction.  We investigate rigid
body or intramolecular movements of myosin by using direction reporting
extrinsic probes that chemically modify selected side chains on the
cross-bridge, and, fluorescence polarization (FP) and/or electron
paramagnetic resonance (EPR) spectroscopy to detect probe orientation.
The sensitivity of probes (optical or EPR) to protein rotation depends
critically on the orientation of the probe in the protein-fixed reference
frame due to ambiguity in the orientation detection techniques.  We may
reduce the ambiguity by combining data from different probes that are
variously oriented relative to the protein using a proven formalism for
mapping global rotations of proteins in assemblies.  We will extend this
method by: (i) investigating local order changes by correlating data from
probes of spatially separated sites, (ii) boosting the angular resolution
of the probe angular distributions to the theoretical limit, and (iii)
introducing and studying the structure of a new class of probes that are
luminescent and paramagnetic (L/P).  To elucidate the mechanism of
protein interaction that results in muscle shortening we will rely on our
increasingly well resolved maps of steady-state cross-bridge order and on
our ability to distinguish local order changes from global changes.  FP
and EPR have time-resolved analogues to investigate rotational dynamics
of cross-bridges on the submillisecond time domain.  Polarized
fluorescence photobleaching recovery (PFPR) induces an oriented subset of
photobleached probes into the total set of fluorescent probes by an
intense pulse of polarized light.  The bleached region is monitored with
attenuated polarized light and the fluorescence recovery is observed as
unbleached fluorophores rotate and their dipoles align with the
polarization of the monitoring light.  Time-Resolved EPR (TEPR) uses L/P
probes that form free radicals when illuminated with light.  An intense
pulse of polarized light causes the photoselection of an oriented subset
of radicals.  The TEPR signal changes as the oriented spins rotate.  For
PFPR and TEPR the signal intensity relaxes to its steady-state value in a
time characteristic of probe mobility.  PFPR and TEPR investigate probe
movement in the three degrees of rotational freedom.  The combination of
static and dynamic probe order information provides a comprehensive
description ...

## Key facts

- **NIH application ID:** 3159300
- **Project number:** 2R01AR039288-04
- **Recipient organization:** MAYO CLINIC ROCHESTER
- **SAM.gov UEI:** Y2K4F9RPRRG7
- **Principal Investigator:** Thomas P Burghardt
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 1993
- **Award amount:** $165,113
- **Award type:** 2
- **Project period:** 1990-01-01 → 1996-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/3159300

## Citation

> US National Institutes of Health, RePORTER application 3159300, MOLECULAR ANGLE TRANSITIONS IN MUSCLE (2R01AR039288-04). Retrieved via MORVS 2026-10-25 from https://api.morvs.ai/grant/nih/3159300. Licensed CC0.

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