Freezing of rat-liver lysosomes to -196 degrees C in the presence and absence of dimethylsulphoxide.

Abstract

The latency of acid phosphatase and β‐glucuronidase in homogenates of rat liver, prepared in 0.25 M glycerol‐2‐phosphate (pH 7.0), decreased after freezing to –196 °C. The latencies obtained were virtually independent of cooling rate in the range of 2–225 °C/min and the latency of acid phosphatase always suffered a greater decrease than that of β‐glucuronidase.The fall in latency was always less in the presence of 7.5% (1.06 M) dimethylsulphoxide and and the protection afforded to the latency of acid phosphatase was greater than that given to β‐glucuronidase. The sedimentability of both enzymes responded to freezing in a manner similar to that found for latency.The sedimentability of acid phosphatase decreased after exposure to high concentrations of sucrose or glycerol‐2‐phosphate. We suggest that this response, as well as the decrease in latency found after freezing and thawing, results from osmotic pressure gradients which arise when normally non‐penetrating molecules enter the lysosomes under a high concentration gradient.The decrease in sedimentability of acid phosphatase after exposure to high concentrations of glycerol‐2‐phosphate was accompanied by a decrease in the specific total activity of the enzyme and it appears that this enzyme is readily inactivated in the presence of high concentrations of this substrate.