GLUCOSE AND GLYCOGEN METABOLISM IN HUMAN EPIDERMIS

[摘要] Data on substrate concentrations and on the maximal activities of several enzymes involved in glucose metabolism and glycogen formation and breakdown have been presented. These represent an initial step towards an understanding of the formation and breakdown of glycogen. These findings combined with those of other workers indicate that glucose within the cell is converted (at approximately 0. 5 m[mu]m/min. /mg epidermis) by hexokinase to glucose-6-phosphate. The rate of this reaction is controlled mainly by the tissue concentration of ADP [adenosine diphosphate] and inorganic phosphate. The glucose-6-phosphate is utilized by 4 different enzymes. Approximately 75% is converted to fructose-6-phosphate, 5% to 6-phospho-gluconate, 5% to G-l-P and UDPG [uridine diphosphoglucose] and about 15% is broken down to free glucose. Of the 5% (0. 025 m[mu]m/min. /mg) going to UDPG formation, the majority proceeds to glycogen formation and only a fraction is channeled into uronic acid formation. Glycogen synthesis (by glycogen synthetase) and its breakdown (by phosphorylase) presumably occur at equal rates which maintains the tissue concentration of glycogen at about 465 m[mu]g/mg. These enzymes of glucose metabolism are found in epidermis in much greater concentrations than those necessary to reproduce in vivo reaction rates. Some of the possible reasons for the differences between the in vivo rates and the in vitro rates were discussed. Glycogen formation and breakdown in epidermis seems to be an active process, with the potentiality of even greater activity (based on theenzyme activities measured). Comparison of these data with similar data from pathological and experimental situations should yield valuable clues to the mechanisms which control these enzymes.