Background:It is generally accepted that the glyoxylate cycle exists in microorganisms and higher plants but absent in higher animals. The hypothesis of the glyoxylate cycle in the tissues of higher animals with a high level of physiological activity was first proposed by Kondrashova and Rodionova in 1971. The goal of this work was to verify this in newborn rats, which possess a 2.5-fold higher physiological activity and oxygen consumption rate than adult rats.Material/Methods:Newborn (7-day-old) and adult rats were used for this experiment. The activities of the key enzymes of the glyoxylate cycle (isocitrate lyase and malate synthase) were measured by HPLC and spectroscopic methods.Results:The activities of isocitrate lyase and malate synthase were found in the liver homogenates prepared from newborn rats, but not from adult rats. The activities of the enzymes common to both the Krebs cycle and the glyoxylate cycle (citrate synthase, aconitase, and malate dehydrogenase) were 20–40% higher in newborn than in adult rats.Conclusions:These data indicate the existence of the glyoxylate cycle in animal tissues.

Keywords: Aconitate Hydratase - metabolism, Citrate (si)-Synthase - metabolism, Glyoxylates - metabolism, Isocitrate Lyase - metabolism, Malate Dehydrogenase - metabolism, Malate Synthase - metabolism, Aconitate Hydratase - metabolism, Aging - physiology, Animals, Newborn, Chromatography, High Pressure Liquid, Citrate (si)-Synthase - metabolism, Citric Acid Cycle, Glyoxylates - metabolism, Isocitrate Lyase - metabolism, Liver - metabolism, Malate Dehydrogenase - metabolism, Malate Synthase - metabolism