α-Crystallin protects human arginosuccinate lyase activity under freeze–thaw conditions

Suppression of protein inactivation during freezing by minimizing pH changes using ionic cryoprotectants

Freezing and lyophilization are often used for stabilization of biomolecules; however, this sometimes results in partial degradation and loss of biological function in these molecules. In this study we examined the effect of freezing-induced acidity changes on denaturation of the model enzyme haloalkane dehalogenase under various experimental conditions. The effective local pH of frozen solutions is shown to be the key causal factor in protein stability. To preserve the activity of frozen-thawed enzymes, acidity changes were prevented by the addition of an ionic cryoprotectant, a compound which counteracts pH changes during freezing due to selective incorporation of its ions into the ice. This approach resulted in complete recovery of enzyme activity after multiple freeze-thaw cycles. We propose the utilization of ionic cryoprotectants as a new and effective cryopreservation method in research laboratories as well as in industrial processes.

The effects of freeze-thaw on β-trace protein and β2-microglobulin assays after long-term sample storage

OBJECTIVES

To evaluate the effect of a freeze-thaw cycle on β-trace protein (βTP) and β2-microglobulin (β2M).

DESIGN AND METHODS

We compared βTP and β2M concentrations before and after a single freeze-thaw cycle in long-term stored samples from 172 participants of the Third National Health and Nutrition Examination Survey (NHANES III).

RESULTS

Measurements of βTP and β2M before and after freeze-thaw were highly correlated with Spearman's coefficients of 0.90 and 0.99, respectively. Serum concentrations of βTP were slightly lower after freeze-thaw (-0.05 mg/L, P=0.006). Measurements of β2M did not differ before and after freeze-thaw (P=0.35).

CONCLUSIONS

βTP and β2M measurements were robust to a single freeze-thaw cycle, although β2M appeared more stable than βTP. These results have implications for future studies of these biomarkers.