The hydrolysis of disodium-p-nitrophenyl phosphate (catalyzed by alkaline phosphatase) in frozen sugar and maltodextrin solutions was studied, with emphasis on how the rate of hydrolysis could be related to the glass transition temperature (Ti). Reaction rates decreased with storage temperature and approached zero at temperatures below -15°C. Arrhenius plots of the data were non-linear, and the slopes of the best-fitting lines differed from one solution to another. The data also did not fit the equation of Williams et a1 (J Am Chem SOC 77 (1955) 3701-3706) that describes diffusional processes as a function of the temperature difference ( T -Ti). However, when placed into similarly composed groups, log (rate) was linearly correlated with the temperature difference ( T -Ti).
The rates of diffusion-controlled processes in a frozen system can be influenced by the presence of glassy states. One characteristic of cryostabilization by this mechanism is a change in the temperature dependence of reaction rates at the Ts' of the system. The cryostabilization behavior of solutes such as maltodextrin, carboxymethylcellulose (CMC), and sucrose was studied. Three different model reaction systems (enzyme hydrolysis, protein aggregation, and non-enzymatic oxidation) were used. Maltadextrin had a consistent pattern of cryostabilization behavior at temperatures ranging from -3°C to -20°C for all three model systems. Significant retardation effects were evident in the temperature range corresponding to its glassy states. Sucrose did not show a stabilizing effect in the non-proteinaceous model system (the non-enzymatic oxidation reaction). This could partly be due to the absence of the glassy state, since the storage temperatures were above its Ts'. However, in the protein aggregation model system, sucrose was an excellent stabilizer in protecting actomyosin from aggregation. This may be explained by a "solute exclusion" mechanism. CMC did not show any stabilizing effect in the protein aggregation and non-enzymatic oxidation model systems studied, even though it has a Ts' as high as that of maltodextrin. These results demonstrated that although the presence of a glassy state may well l1ave a retarding effect on the rates of diffusion processes, just knowing the Ts' of a polymer is not sufficient for prediction of its stabilization effect in a frozen system.
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