Factors Affecting the Activity of Pentose Phosphatemetabolizing Enzymes in Rat Liver

Abstract

A direct spectrophotometric method for the assay of pentose phosphate-metabolizing enzyme activity, also referred to as transketolase activity, is described. This method was used to study the effect of diets and hormones on the liver activity of this enzyme system. High protein, high fructose, and a starvation-refed regimen all produced significant increases in pentose phosphate-metabolizing enzyme activity. Administration of hydrocortisone or cortisone also caused increases and feeding iodinated casein or thyroxine administration had a negligible effect on the activity of this system. A 4-day fast, diabetes, adrenalectomy, and hypophysectomy all caused significant decreases in liver pentose phosphate-metabolizing enzyme activity. Both vitamin-free and thiamine-free diets produced large decreases in the activity of this system, whereas a pyridoxine-free diet causd only a slight decrease in activity. The addition of oxythiamine to the thiamine-free diet caused a further decrease in activity of the pentose phosphate-metabolizing enzymes.