Exposure of hydrophobic amino acid residues from actomyosin on freezing - Reconfirmation by fluorometry.

After freezing overnight at-2°C, various actomyosin (AM) and actin (Ac) solutions underwent the fluorometric measurements in the presence of sodium 8-anilino-1-naphthalene sulfonate (exciting wavelength: 365nm, emission wavelength: 470nm). For AM solutions, their fluorometric intensity was increased on freezing. This increment was mare remarkable for fish than for warm blooded animal. However, the increase in fish was depressed by the addition of 10% sucrose or 0.2% monosodium glutamate. The intensity of fish Ac was hardly increased on freezgng. Therefore, it is suggested that the hydrophobic amino acid residues of AM are exposed on freezing, and this is more remarkable for fish than for warm blooded animal, but their exposure for fish is suppressed by cryoprotectants. This conclusion is the same as that derived from the previously reported SDS adsorption method. Furthermore, it is also suggested that their exposure from AM is due to myosin rather than to Ac.