Abstract
In thepreviousreport effects ofgamma-irradiation on the gelation of fish actomyosin were investigated. It has been demonstrated that a remarkable change from sol to gel of actomyosin solution differs among the various conditions such as the concentration of actomyosin or KCl as a solvent, the irradiation dosages, the presence of oxygen or nitrogen, and the addition of oxidants or an antioxidant. Moreover, from the results of polarographic observation of protein waves and the protein solubility in centrifugal preparation of irradiated actomyosin, it has been suggested that the gel formation is probably due to the interaction of sulfhydryl groups and a higher macromolecule of actomyosin formed during irradiation.
In this paper to obtain some aspects on the mechanism of the gel formation of irradiated actomyosin, the sulfhydryl-disulfide exchange reactions between thiamines and actomyosin were ascertained by paper chromatography, paper electrophoresis and fluorometry as follows.
1) The bound thiamine with protein and free thiaminewere produced by the reaction of thiamine disulfide (TDS) with actomyosin at pH 7.3, 37°C for 60 minutes, but not formed by the reaction with the actomyosin treated with SH-masked reagents such as p-chloromercuribenzoate or iodo-acetic acid (Figs. 1 and 2). Therefore, it is supposed that the above reaction is caused by the SR-SS exchange between the sulfhydryl group of actomyosin and the disulfide group of TDS.
2) Thiol-type thiamine was unreactive at pH 7.3 because of the probable uncleavage of thiol on the thiazole ring whereas TDS reacted easily with actomyosin regardless of irradiation dosages (Figs. 3 and 4).
3) In the pH ranges 8-9 the reactivity of irradiated actomyosin and thiol-type thiamine increased extremely with alkalifing pH and reached constantly above pH 10 (Fig. 5), while at pH 10 the amounts of bound thiamine increased almost linearly with increasing irradiation dosages up to about 100, KR (Fig. 6).
4) The reactivity of thiol-type thiamine with the irradiated actomyosin, in the presence of oxygen, in which case the actomyosin was little gelled, was higher than that in the presence of nitrogen (Fig. 7).
From these results, it is suggested that the interchange from thiol to disulfide bond in the actomyosin molecule will occurs, while it is doubtful if such interchange is of great importance for the maintenance of specific gel formation by irradiation.
