Fred B. Stifel

Dietary regulation of glycolytic enzymes I. Adaptive changes in rat jejunum

Abstract 1. 1. The effects of dietary fructose, sucrose, glucose, casein and fasting upon the activity of several glycolytic enzymes [fructokinase (ketohexokinase, EC 2.7.1.3), hexokinase (ATP: D -hexose 6-phosphotransferase, EC 2.7.1.1), glucokinase (ATP: D -hexose 6-phosphotransferase, EC 2.7.1.2), Fru- I -P aldolase (ketose- I -phosphate aldehyde-lyase, EC 4.1.2.7), Fru- I ,6-P 2 aldolase (fructose- I ,6-diphosphate D -glyceraldehyde-3-phosphate-lyase, EC 4.1.2.13) and aldose reductase (alditol:NADP+ oxidoreductase, EC 1.1.1.21)] were studied in the jejunum of rats. 2. 2. Individual sugars (glucose, sucrose and fructose) have specific carbohydrate effects on certain jejunal glycolytic enzymes. Fructose had a specific adaptive effect upon fructokinase and Fru- I -P aldolase, while glucose exerted its adaptive effect upon hexokinase and glucokinase. The addition of calories in the form of casein to fasted rats caused a non-specific increase in the activity of all jejunal glycolytic enzymes studied. 3. 3. Changes in rat jejunal glycolytic enzymes due to diet reflect those in rat liver. 4. 4. The ratio of Fru- I ,6-P 2 / Fru- I -P adolase activities in the liver activities was close to 1.0 for all diets whereas in the jejunum the ratio of activities is altered by diet. The fact that the jejunal activity ratio was lower than I in fructose-fed rats suggests that the intestine may contain an aldolase with different properties from those in other tissues.

Rapid reciprocal changes of rat hepatic glycolytic enzymes and fructose-1,6-diphosphatase following glucagon and insulin injection in vivo

Abstract Glucagon and insulin given intravenously produced rapid reciprocal changes in the activity of phosphofructokinase (PFK), pyruvate kinase (PK) and fructose diphosphatase (FDPase) in rat liver. Fructose diphosphate aldolase did not change. Glucagon increased FDPase and decreased PFK and PK activity. Insulin decreased FDPase and increased PFK and PK activity. The glucagon effect was associated with a marked increase in hepatic cyclic adenosine 3′,5′-monophosphate (cyclic AMP) concentrations. Insulin did not significantly alter hepatic cyclic AMP concentrations.

Dietary regulation of glycolytic enzymes: III. Adaptive changes in rat jejunal pyruvate kinase, phosphofructokinase, fructosediphosphatase and glycerol-3-phosphate dehydrogenase

Abstract 1. 1. The effects of dietary fructose, glucose, casein and fasting upon the activity of six enzymes involved in carbohydrate metabolism (phosphofructokinase (ATP: d -fructose-6-phosphate 6-phosphotransferase, EC 2.7.1.11), pyruvate kinase (ATP: pyruvate phosphotransferase, EC 2.7.1.40), fructosediphosphatase ( d -fructose-1,6-diphosphate 1-phosphohydrolase, EC 3.1.3.11), glycerol-3-phosphate dehydrogenase ( l -glycerol 3-phosphate: NAD oxidorectase, EC 1.1.1.8), glucokinase (ATP: d -hexose 6-phosphotransferase, EC 2.7.1.2), and hexokinase (ATP: d -hexose 6-phosphotransferase, EC 2.7.1.1)) were studied in the jejunum and liver of rats. 2. 2. Individual sugars (fructose and glucose) have specific carbohydrate effects on certain jejunal glycolytic enzymes. Fructose had a specific adaptive effect upon pyruvate kinase, phosphofructokinase and glycerol-3-phosphate dehydrogenase, while glucose exerted its maximum adaptive effect upon hexokinase and glucokinase. The addition of calories in the form of casein to fasted rats caused a nonspecific increase in the activity of these same enzymes. 3. 3. Fructosediphosphatase activity was highest in the fasted rats and decreased in order on the casein, fructose and glucose diets. The fructosediphosphatase to phosphofructokinase activity ratio was highest in the fasted rats, lower on the casein diet and lowest on glucose and fructose diets. 4. 4. Changes in rat jejunal enzymes due to diet reflect those in rat liver.

The dietary regulation of the glycolytic enzymes II. Adaptive changes in human jejunum

Abstract The specific effects of dietary sugars on human jejunal glycolytic enzymes were studied in normal volunteers and fasting obese patients. Fructokinase (ketohexokinase, EC 2.7.1.3), Fru- I -P aldolase (ketose- I -phosphate aldehyde-lyase, EC 4.1.2.7), hexokinase (ATP: D -hexose 6-phosphotransferase, EC 2.7.1.1), glucokinase (ATP: D -hexose 6-phosphotransferase, EC 2.7.1.2), and Fru- I ,6-P 2 aldolase (fructose- I ,6-diphosphate D -glyceraldehyde-3-phosphate-lyase, EC 4.1.2.13) were measured. Fructose feeding had a specific effect on fructokinase and Fru- I -P aldolase whereas glucose had its major effect on hexokinase and glucokinase. Sucrose gave results intermediate between glucose and fructose. Carbohydrate-free diets gave results intermediate between fasting and carbohydrate diets. There were different responses of the Fru- I -P and Fru- I ,6-P 2 aldolases to different dietary sugars. These data indicate that specific dietary sugars can increase specific jejunal glycolytic enzymes in the human.

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.

Dietary regulation of glycolytic enzymes IV. Differential hormonal effects in male and female rat jejunum

1. 1. The effects of oral progesterone, diethylstilbestrolm 17β-estradiol and testosterone (100 μg/100 g body wt.) upon the activity of five enzymes involved in carbohydrate metabolism (phosphofructokinase (ATP:D-fructose-6-phosphotransferase, EC 2.7.1.11), pyruvate kinase (ATP: pyruvate phosphotransferase, EC 2.7.1.40), fructosediphosphatase (D-fructose-1,6-diphosphate 1-phosphohydrolase, EC 3.1.3.11), hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1) and Fru-1,6-P2 aldolase (fructose-1,6-diphosphate D-glyceraldehyde-3-phosphate-lyase, EC 4.1.2.13)) were studied in the jejunum of both male and female rats. 2. 2. In male rats, jejunal phosphofructokinase activities were in the following order: testosterone > estradiol > diethylstilbestrol > progesterone > control P progesterone, diethylstilbestrol, estradiol > testosterone (P × 0.01). No differences were noted in the hexokinase or Fru-1,6-P2 aldolase activities in the five groups. 3. 3. In female rats, jejunal phosphofructokinase activities were in the following order: estradiol > diethylstibestrol > testosterone > progesterone > control (P estradiol > progesterone > testosterone > diethylstilbestrol (P < 0.01). No differences were noted in the hexokinase or Fru-1,6-P2 aldolase activities in the five groups. 4. 4. In female rats, bothe progesterone and testosterone blocked the adaptive increases in jejunal phosphofructokinase and pyruvate kinase activities caused by estradiol alone. In male rats, in contrast, estradiol blocked the testosterone-produced adaptive increases in the jejunal phosphofructokinase and pyruvate kinase activities. 5. 5. These data imply that the response of the jejunal enzymes to sex hormones is determined in part by the sex of the animal.

Dietary regulation of glycolytic enzymes: VI. Effect of dietery sugars and oral folic acid on human jejunal pyruvate kinase, phosphofructokinase and fructosediphosphatase activities

Abstract 1. 1. The effects of dietary sugars and oral folic acid on the activities of human jejunal pyruvate kinase (ATP: pyruvate phosphotransferase, EC 2.7.1.40), phosphofructokinase ATP: D -Fru -6-P- phosphotransferase , EC 2.7.1.11) and frutosediphosphatase ( D -Fru -1,6-P 2 1- phosphohydrolase , EC 3.1.3.11) were studied in two normal volunteers and three obese patients. 2. 2. The activities of pyruvate kinase and phosphofructokinase are highest on dietary fructose and decrease in order on glucose, carbohydrate-free and fasting regimens. Fructosediphosphatase activities are highest with fasting and decrease in order with carbohydrate-free, fructose and glucose diets. The fructosediphosphatase to phosphofructokinase ratio, an estimate of the net direction of the glycolytic and gluconeogenetic pathways on the different diets, is highest with fasting and decrease in order on the carbohydrate-free, glucose and fructose diets. 3. 3. In contrast with the dietary sugars, oral folic acid produced a marked increase in the activities of all three enzymes. 4. 4. Therefore, oral folic acid and dietary sugars can regulate the activities of human jejunal gluconeogenetic, as well as glycolytic, enzymes.

The Rapid Changes of Hepatic Glycolytic Enzymes and Fructose-1, 6-Diphosphatase Activities after Intravenous Glucagon in Humans

Glucagon (0.04-0.09 mg/kg/min) was given intravenously for either 2 or 3 min to eight patients with fasting-induced hypoglycemia. One child had hepatic phosphorylase deficiency, two children had glucose-6-phosphatase deficiency, two children had debrancher enzyme (amylo-1,6-glucosidase) deficiency, and two children and one adult had decreased hepatic fructose-1,6-diphosphatase (FDPase) activity. Liver biopsy specimens were obtained before and immediately after the glucagon infusion. The glucagon caused a significant increase in the activity of FDPase (from 50+/-10.0 to 72+/-11.7 nmol/mg protein/min) and a significant decrease in the activities of phosphofructokinase (PFK) (from 92+/-6.1 to 41+/-8.1 nmol/mg protein/min) and pyruvate kinase (PK) (from 309+/-39.4 to 165+/-23.9 nmol/mg protein/min). The glucagon infusion also caused a significant increase in hepatic cyclic AMP concentrations (from 41+/-2.6 to 233+/-35.6 pmol/mg protein). Two patients with debrancher enzyme deficiency who had biopsy specimens taken 5 min after the glucagon infusion had persistence of enzyme and cyclic AMP changes for at least 5 min. One child with glucose-6-phosphatase deficiency was given intravenous glucose (150 mg/kg/min) for a period of 5 min after the glucagon infusion and biopsy. The plasma insulin concentration increased from 8 to 152 muU/ml and blood glucose increased from 72 to 204 mg/100 ml. A third liver biopsy specimen was obtained immediately after the glucose infusion and showed that the glucagon-induced effects on PFK and FDPase were completely reversed. The glucagon infusion caused an increase in hepatic cyclic AMP concentration from 38 to 431 pmol/mg protein but the glucose infusion caused only a slight decrease in hepatic cyclic AMP concentration (from 431 to 384 pmol/mg protein), which did not appear to be sufficient to account for the changes in enzyme activities. Hepatic glucose-6-phosphatase and fructose-1,6-diphosphate aldolase activities were not altered by either the glucagon or the glucose infusion in any patients. Cyclic AMP (0.05 mmol/kg) was injected into the portal vein of adult rats and caused enzyme changes similar to those seen with glucagon administration in humans. Our findings suggest that rapid changes in the activities of PFK, PK, and FDPase are important in the regulation of hepatic glycolysis and gluconeogenesis, respectively, in humans and that cyclic AMP may mediate the glucagon- but probably not the glucose-insulin-induced changes in enzyme activities.

Fructose-1,6-diphosphatase deficiency, hypoglycemia, and response to folate therapy in a mother and her daughter

Abstract Symptomatic fasting and reactive hypoglycemia in association with low iejunal and hepatic fructose-1,6-diphosphatase (FDPase) activity were found in an adult patient and her 19-month-old daughter. Plasma glucose response to glycerol ingestion was abnormal in both, showing little change in the adult and a decline in the child. FDPase activity was low in tissues from both patients. This reduced enzyme activity defines a new variant of the fructose-1,6-dipphosphatase deficiency state(s) which is mild in its manifestations and thus more resistant to the hypoglycemia-provoking effects of fructose and alanine. No difference was detected between the FDPase from these patients and unaffected individuals by polyacrylamide gel electrophoresis. The K m of the jejunal enzyme for fructose diphosphate in the adult was similar to the normal control. Glucagon rapidly increased the activity of hepatic FDPase in both patients. Folic acid, 15 mg/day, increased hepatic and jejunal FDPase activity in both patients. After folate therapy, there was improvement in the adults symptoms and improvement in the childs ability to maintain normal plasma glucose levels. The interrelationship between the hypoglycemia, FDPase deficiency, and the response to folate therapy was discussed.

Dietary regulation of glycolytic enzymes IX. The effect of oral, intramuscular and conjugated sex steroids on jejunal glycolytic enzyme activities in normal and castrated male and female rats

Abstract 1. 1. The effects of oral, intramuscular and conjugated sex hormones (progesterone, testosterone and estradiol-17β) upon the activities of four enzymes involved in folate metabolism, (glutamate formiminotransferase (N-formimino- L -glutamate:tetrahydrofolate 5-formiminotransferase, EC 2.1.2.5), serine hydroxymethyltransferase ( L -serine : tetrahydrofolate 5,10-hydroxymethyltransferase, EC 2.1.2.1), methylenetetrahydrofolate dehydrogenase (5,10-methylenetetrahydrofolate : NADP oxidoreductase, EC 1.5.1.5) and formyltetrahydrofolate synthetase (formate : tetrahydrofolate ligase (ADP), EC 6.3.4.3)) were studied in the jejunum of normal and castrated male and female rats. 2. 2. These studies demonstrate that oral sex hormones (estradiol in females, testosterone in males) produce significant adaptive increases (P