INCREASE IN ACID INVERTASE ACTIVITY AND ACCUMULATION OF REDUCING SUGAR IN POTATOES STORED AT LOW TEMPERATURES AND PURIFICATION OF ACID INVERTASE

Abstract

It is well known that storage of potato tubers at chilling temperatures results in an increase in the content of simple sugars, mainly sucrose, glucose, and fructose. We have observed that in Russet Burbank potatoes sucrose is the first sugar to accumulate, followed by a rise in glucose and fructose. The ratio of the increment of glucose to fructose is one, indicating that sucrose is the sole source for the reducing sugars. Our data show that there is a close temporal relationship between the accumulation of reducing sugars and rise in the activity of acid invertase (AI). Purification of combining Con A-Sepharose 4B affinity followed by DEAE-Sephacel ion exchange columns resulted in 144-fold purification of AI. SDS-PAGE indicating that the above procedure resulted in the concentration of 58 kDa polypeptide. IEF electrophoresis revealed the presence of five isoforms of AI with the following pI: 5.16, 5.25, 5.37, 5.55, 5.85. Two-D gel electrophoresis (native-to-denature) showed that a polypeptide of 49.48 kDa was associated with all isoforms of AI. There were also two addition polypeptides with 37.94 and 20.07 kDa which could be breakdown products of the 58 kDa protein or subunits of AI.