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The birth of the sliding ribbon theory: How was it proposed independently by two groups of scientists?
The sliding ribbon theory is an important theory to explain the mechanism of muscle contraction, which is based on the fact that muscle proteins slide over each other to produce movement. According to this theory, myosin (thick filaments) in a muscle fiber slide past actin (thin filaments) during muscle contraction, while the lengths of these two sets of filaments remain relatively constant. The theory was independently proposed in 1954 by two research teams, Andrew Huxley and Rolf Niedergelke of Cambridge University, and Hugh Huxley and Jane Hansen composition.
The theory was originally conceived by Hugh Huxley in 1953 and proposed by Andrew Huxley and Niedergelke as a "very attractive hypothesis".
Before the 1950s, there were several competing theories to explain muscle contraction, including electrical attraction, protein folding, and protein modification. The new theory proposes a concept called cross-bridge (traditionally called swinging cross-bridge, now mainly called cross-bridge loop), which explains the molecular mechanism of sliding ribbons. The cross-bridge theory states that actin and myosin form a protein complex (traditionally called actin-myosin) by attaching the myosin head to the actin filament, so that there is a cross between the two filaments. A cross bridge is formed between them.
Historical Background Early researchIn the early 1870s, German scientist Willy Kuch first discovered the muscle protein myosin, which was extracted and named in 1864. In 1939, the Russian husband-and-wife team Vladimir Alexandrovich Engelhardt and Milisa Nikolaevna Liubinmova discovered that myosin has the properties of an enzyme (called ATPase) , which can break down ATP to release energy. After Hungarian physiologist Albert St. George won the Nobel Prize in 1937 for his work on vitamin C and maleic acid, he turned his attention to muscle physiology. St. George demonstrated in 1942 that ATP is the energy source for muscle contraction and observed that muscle fibers containing myosin B shortened in the presence of ATP, whereas myosin A did not, an experience he later described as "One of the most exciting moments of my life."
Origin of the theory
When Hugh Huxley received his PhD from Cambridge University in 1952, St George had already shifted his career towards cancer research. In September 1952, Huxley arrived at the laboratory of Francis O. Schmidt at MIT and in January 1953 he was joined by another British postdoctoral researcher, Jane Hansen. Using X-ray diffraction, Huxley hypothesized that muscle proteins, particularly myosin, form structured ribbons that give rise to sarcomeres (a segment of a muscle fiber). Their main aim was to study these ribbons in detail using electron microscopy. They quickly discovered and confirmed the ribbon nature of muscle proteins.
The Sliding Ribbon Theory
The sliding ribbon theory originated from two papers published in the journal Nature on May 22, 1954, titled "Structural changes in muscle during contraction." While their conclusions are fundamentally similar, the experimental data and proposals are different.
The first paper, co-authored by Andrew Huxley and Rolf Niedergelke, is titled "Interference Microscopy of Living Muscle Fibers." According to the paper, the I-band is made up of actin filaments, while the A-band is mainly made up of myosin filaments, and during contraction, the actin filaments move between the myosin filaments.
The second paper, written by Hugh Huxley and Jane Hansen, is titled "Changes in cross-striation during muscle contraction and extension and their structural interpretation." This one is more detailed than the first, based on studies of rabbit muscle using phase contrast and electron microscopy.
Acceptance and Consequences
Despite the strong evidence, the sliding ribbon theory did not gain support in the following years. St. George himself refused to believe that myosin filaments were restricted to thick filaments (A bands). Only in 1957, Huxley in the United States gave the new electron microscope confirmed the overlapping nature of the ribbons.
It was not until a 1972 conference at Cold Spring Harbor Laboratory that the theory and its evidence gained general acceptance. Attendees remembered Hansen shouting in response to criticism: "I know I can't explain the mechanism, but sliding is a fact."
As evidence accumulated, Huxley formally proposed the mechanism of the sliding ribbon, which is now called the cross-bridge loop.
These studies not only changed the face of muscle physiology, but also led to future explorations of more complex biological mechanisms. This groundbreaking theory makes us wonder: How many other undiscovered biological mechanisms are there, waiting for people with lofty ideals to reveal?
