UC San Diego

This thesis relates to a working hypothesis that inhibition of three isozymes rabbit muscle PFK-1, LDH and AK by ascorbate shuts down glycolysis pathway and facilitates glycogen storage in resting muscle; when muscle is active these isozymes combine with skeletal muscle proteins such as aldolase and actin and are protected from inhibition by ascorbate and glycolysis proceeds. Dibutyryl- (DB), dipalmityl- (DP), palmityl- (P), and stearyl- (S) fatty acid derivatives of ascorbic acid (AA) were shown to plot as irreversible inhibitors of rabbit muscle PFK-1 and LDH. Inhibition potencies of all these inhibitors on PKF-1, LDH and AK were measured as I50 values, concentrations of inhibitor required for 50% inhibition of enzyme activity, and compared to I50 values for AA. All AA-fatty acid derivatives were more inhibitory than AA except for AADB, which was less inhibitory for PFK -1 but the most inhibitory for LDH. Most AA fatty acid derivatives showed inhibitory effect on AK but were not better inhibitors than AA. Studies on substituents of AA fatty acid inhibitors suggested double bond in the lactone ring of AA and its derivatives contribute to the inhibitory characteristics. Similar to AA inhibitions of PFK-1 and LDH, rabbit muscle aldolase protected against activity losses due to dilution and AA-fatty acid derivatives. AMP, a PFK-1 activator, also demonstrated protecting PFK-1 from AA and its derivative inhibitors. Inhibition properties of AA-fatty acid derivatives shown here are discussed in terms of other possible fatty acid derivatives and possible therapeutic values in cancer and diabetes