SUMMARY—Sucrose hydrolysis catalyzed by invertase was studied over the temperature range 12 to −22°C in solutions of various concentrations. Freezing resulted in a marked decrease in invertase activity. Factors considered as having a possible role in the inhibition of invertase by freezing were: (1) the presence of ice crystals, (2) the increased concentration of solutes resulting from ice formation, and (3) a temperature effect in excess of that predicted from the Arrhenius equation (secondary temperature effect). It was shown that ice crystals formed at the rate used in this study had no effect on invertase activity, and that the decrease in invertase activity at sub‐zero temperatures was quantitatively accounted for by the concentration effect and the secondary temperature effect. High levels of sucrose and buffer (ionic strength) were found to inhibit invertase activity. Sucrose hydrolysis catalyzed by acid (HCI) was studied over the temperature range 12 to –16.5°C, and an Arrhenius plot of the data was linear between 12 and ‐7°C. Once the solution was frozen (below –6.8°C), the effect of temperature on the reaction rate constant no longer obeyed the Arrhenius equation, and the reaction rate constant was found to exhibit a maximum between –8.5 and –16.5°C. The rate of sucrose hydrolysis catalyzed by acid was influenced by cooling and conventional freezing in a manner quite different from that observed with invertase
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