Effect of Dietary Carbohydrate on Glucokinase and Mannokinase Activities of Various Rat Tissues

Publisher Website
Google Scholar
Abstract
Glucokinase activities were determined in 9 rat tissues — liver, brain, muscle, kidney, small intestine, heart, spleen, adipose tissue and mammary gland. Significant amounts of glucokinase activity were particle-bound in brain (40 to 55%), in heart (50 to 60%) and in mammary gland (40%). In the other tissues, almost all of the activity appeared in the particle-free supernatant fraction. Except for a minor response by small intestine, liver was the only tissue in which glucokinase activity responded significantly to nutritional treatment of the rat. Evidence for the existence of 2 distinct enzymes capable of phosphorylating glucose was obtained from a study of the Km (glucose) values for the enzymes in the particle-free supernatant fraction of rat liver. The hepatic enzyme with a high Km value for glucose was shown to adapt to dietary treatment, whereas the hepatic glucokinase with a low Km for glucose was non-adaptable. Mannokinase activities were determined in brain, liver and mammary gland. The rates at which brain, liver and mammary gland phosphorylated mannose were 33, 27 and 26%, respectively, of those observed for glucose.