mechanism of formation of gels from myosin molecules

Heat-set myosin gels form the basis of the adhesive that binds particles of meat together in meat products. The manner in which a gel network is formed from myosin has been investigated by studying the aggregates produced when dilute solutions of rabbit skeletal myosin molecules in 0.6 m KC1, 20 mM potassium phosphate, pH 6.5, were heated at a single temperature between 30 and 60 degrees C. The aggregates have been examined by transmission electron microscopy after either negative staining or rotary shadowing. After heating at 30 degrees C for 10 min, no change in structure is detected. After heating at 35 degrees C for 30 min, the two heads of some myosin molecules coalesce and some dimers are formed by aggregation through the heads. After heating at 40 degrees C for 30 min, up to about 13 myosin molecules aggregate through their heads to form a globular mass up to 60 nm across with the tails radiating outwards. At higher temperatures such head-linked oligomers aggregate further. At 48 degrees C oligomers coexist with aggregates formed by the coalescence of two or more oligomers. In such aggregates the globular masses are in close proximity and tails radiate from them. After heating myosin at 50 degrees C, aggregates are formed by the coalescence of more oligomers and the tails are seen only indistinctly. At 6O degrees C the particles formed contain a large number of globular masses and are typically 100 to 200 nm across, occasionally up to 1 micrometer. It is possible that the globules making up the strands of the gel networks in scanning electron micrographs are composed of similar particles. It is suggested that these globules are formed by head-head interactions but that tail- tail interactions may be important in forming the strands and cross-links of the gel network. When a heat-set myosin gel is compacted by centrifugation, the supernate contains essentially all the LC1 and LC3 light chains of the parent molecule but only a small fraction of the LC2 light chains. We suppose that dissociation of the LC1 and LC3 chains from the heads creates hydrophobic patches which cause intramolecular and intermolecular head association.