“Comparison of r-Phosphofructokinase (r-PFK-1) Enzyme Inhibition by Ascorbic-6-Butyrate (AAB), Ascorbic Acid-6-Palmitate (AAP) and Ascorbic Acid-6-Stearate (AAS)”

A number of research studies on fatty acid derivatives of Ascorbic Acid (AA) have yielded interesting results such as: antimetastatic action of certain cancers, and inhibition of r-Phosphofructokinase (PFK-1) which helps regulate glycolysis and the metabolism of glucose. Other studies have concluded that cancer cells have a greater survival dependence on glucose than normal cells. Therefore, inhibition of glycolysis should effect cancer cells greater than normal cells. Previous studies found that the sixteen and eighteen carbon side chain derivatives, ascorbic acid-6-palmitate (AAP) and ascorbic acid-6-stearate (AAS),  decrease PFK-1 enzyme activity twelve fold and ten fold respectively, relative to ascorbic acid (AA). Based on this observation, our hypothesis was that shortening the side chain and reducing the lipophilic characteristics should diminish hydrophobic interactions with r-PFK-1 and lower the inhibition. To test our assumption, we synthesized Ascorbic Acid-6-butyrate (AAB) according to the method of Tanaka and Yamamoto. r-PFK-1 enzyme was purified from frozen rabbit muscle employing centrifugation and ion-exchange filtration. Inhibitions were carried out in buffered solutions of 95% ethanol.  Our results show that AAB inhibited r-PFK-1 two-times greater than ascorbic acid (AA) but was only 0.16 as inhibitory as AAP, and only 0.20 as inhibitory as AAS. Under our experimental conditions, 95% ethanol, and methyl and ethyl butyrates, palmitates, and stearates showed no significant inhibitions of r-PFK-1. From the results, we conclude that the side chain length and lipophilic characteristics of the ascorbic fatty acid derivatives may be the major contributors in the observed inhibitions of r-PFK-1 activity.