An investigation of the effect of cryoprotective agents on intermolecular disulfide formation
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"A cryoprotective compound is one which prevents or decreases injury caused by freezing living material. Several of these agents are known. It is not known why or how cryoprotective agents protect. It is the purpose of this study to investigate one possible explanation, on the basis of the sulfhydryl hypothesis. The major question to be answered by this study is: Do cryoprotective compounds which prevent damage in a living system due to freezing also protect proteins against intermolecular disulfide bond formation? The model system Thiogel was used because of ease of measurement of intermolecular SS formation and lack of complicating factors found in living systems. Sulfhydryl groups on the protein molecules of Thiogel are oxidized slowly in air to disulfide bonds. Freezing increases the rate of this oxidation. Whan the Thiogel is frozen slowly, the ice forms as a shell on the gel surface. It is the removal of water from the Thiogel to this ice shell which causes the increase in the rate of formation of disulfide bonds. As the water is removed the protein molecules come closer together, catalyzing the oxidation reaction. Disulfide bond formation is detected by an increase in the melting point of the gel (13). According to the sulfhydryl hypothesis any substance which would decrease the rate of disulfide bond formation as shown by prevention of a rise in the melting point of the Thiogel would presumably also protect proteins in living cells."--Introduction.
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