Enzymes of Carbohydrate Metabolism in Normal Human Sebaceous Glands

Abstract

Glucose, glycogen, and ATP concentrations were measured in the peripheral and central layers of the sebaceous glands as well as in the epidermis. Both carbohydrates exhibited a decreasing gradient of concentration from the periphery to the center of the glands. No differential distribution of ATP content was found in the sebaceous glands. The periphery of the glands contained 8 m moles glucose, 22 m moles glycogen, and 10 m moles ATP per kg dry weight tissue. The glucose and ATP concentrations were comparable to those in epidermis, whereas on the basis of lipid-free dry weight the amount of glycogen at the periphery was 6.3 times that of epidermis. The total NADP concentration in sebaceous glands was 0.5 m moles/kg dry weight, 78 percent of which was in the reduced form; the total NAD concentration was 1.4 m moles/kg dry weight, 34 percent of which was in the reduced state. Sebaceous glands contained 3 times more NADP nucleotides than epidermis. The ratios of the NAD nucleotides to NADP nucleotides were 3: 1 in the sebaceous glands and 8: 1 in the epidermis. Of the 29 enzymes assayed, the most prominent in the sebaceous glands were α-glycerophosphate dehydrogenase, malic enzyme, alanine amino-transferase, glucose-6-phosphate dehydrogenase, and phosphorylase. Enzyme analyses also demonstrated increased contributions of the pentose phosphate pathway and tricarboxylic acid cycle, a significant role for glycogen metabolism and active glycolysis. The high activities of α-glycerophosphate dehydrogenase and triosephosphate isomerase suggest that triosephosphate is being shifted into α-glycerophosphate for the acylglycerol formation. The high aminotransferase activities suggested an important contribution of amino acid metabolism to the sebaceous glands. The conspicuously high activity of alanine aminotrans-ferase indicates a tissue potential to convert amino acids to pyruvate in sebaceous glands. High malic enzyme and malate dehydrogenase activities suggest a malate shunt, by means of which an ATP-driven transhydrogenation between NADP and cytoplasmic NADH occurs to produce NADPH. Isocitrate dehydrogenase was the most active among the NADP-dependent enzymes and appeared to participate in NADPH production in the sebaceous glands. Acid phosphatase activity was 5 to 7 times greated in the central portion than in the peripheral layers of the sebaceous glands. Three β-glycosidases were distributed more in the center than in the periphery of the glands. High acid phosphatase activity in the central portion of sebaceous glands may reflect its involvement in holocrine secretion.