Regulation of human jejunal glycolytic enzymes by oral folic acid

The effect of oral folic acid on jejunal glycolytic enzyme activity in five fasting obese patients and in three normal male volunteers on a constant 3000 cal diet was studied. The glycolytic enzymes, fructokinase, hexokinase, glucokinase, fructose-1-phosphate aldolase, and fructose diphosphate aldolase, and the disaccharidases, sucrase, maltase, and lactase were measured. In both the fasting patients and the normal volunteers, oral folic acid significantly increased the jejunal glycolytic enzyme activities but had no effect on disaccharidase activity. When oral folic acid was discontinued in the normal volunteers, the glycolytic enzyme activities returned to control values. In the obese patients, refeeding and folic acid caused a further increase in glycolytic enzyme activities above that seen with fasting and folic acid. In contrast to oral folic acid, intramuscular folic acid, oral vitamin B(12), and oral tetracycline had no effect on glycolytic enzyme activities. These studies demonstrate that oral folic acid which is neither a substrate nor a coenzyme of these enzymes, increases human jejunal glycolytic enzyme activity in a specific fashion. This would appear to be an action of oral folic acid which has not been recognized previously.