Glycerol oxidation in rat brain: Subcellular localization and kinetic characteristics

Abstract

The oxidation of [1,3-14C] glycerol to 14CO was measured in slices, whole homogenates, and subcellular fractions of rat brain. In all of these tissue preparations, the Lineweaver-Burk plots of glycerol oxidation were biphasic, yielding two apparent Km and V values. Similar kinetic characteristics were obtained with brain homogenates from guinea pig, mouse, rabbit, monkey, and pig. In other tissues of the rat, including heart, kidney, liver, and skeletal muscle, the Lineweaver-Burk plots for glycerol oxidation were not biphasic but were linear. Heating the brain homogenates for five minutes at 5 degrees C caused a 50% decrease in the rate of oxidation of glycerol without a change in the biphasic double reciprocal plot. The addition of purified glycerol kinase (EC 2.7.1.30) to the homogenate caused an increase in the rate of oxidation and resulted in linear Lineweaver-Burke plot. Brain mitochondria were prepared by two different methods, both of which yielded an enrichment of glycerol oxidation. In contrast, the rate of glucose oxidation was higher in homogenates than in mitochondria, and glucose competed with glycerol as substrate only extramitochondrially. The effects of various metabolic inhibitors suggested the participation of intact, coupled mitochondria, of glycolytic enzymes, and of electron transport in the oxidation of glycerol. The data support the primary localization of glycerol oxidation in nonsynaptic mitochondria in brain and the presence in that organelle of enzymes of the Embden-Meyerhoff pathway or an as yet unidentified system for oxidizing this compound.

A Developmental Study of Glycerol Oxidation by Rat Brain

“…The concentrations of glycerol were 0.1,0.2, 0.5, 1.0, 10.0, and 20.0 m/W and some experiments included 5.0 m/W glycerol. The incu bation conditions were similar to those used in previous experiments (Tildon and Roeder, 1980] which revealed that the rate of M CO, production from labelled glycerol was linear with time up to 2 h and was proportional to protein concentration. rent from that at 2-3 days or any other age trough 24-26 days); bars without common I oi uperscripts are significantly different from cT ach other at the p<0.05 level (e.g.…”

“…Plasma glycerol levels are highest in the early neonatal period in both human in fants [Persson andGentz, 1966: Melichar andWolf, 1967] and rat pups [Vernon and Walker, 1970] and essentially parallel those of the ketone bodies in early development. Glycerol can also be utilized for energy by the adult brain [Goodner et al, 1973: Tildon et ah, 1976Tildon and Roeder, 1980] and glycerol kinase (ATP: glycerol-3-phosphotransferase, EC 2.7.1.30), the initial enzyme of glycerol metabolism, has been shown to be present in brain tissue. Furthermore, this en zyme has a Km that is sufficiently low (2.9-70 ptM) such that glycerol could be a major energy substrate for brain tissue provided sufficient levels of glycerol are present [Jen kins and Hajra, 1976;Tildon et ah, 1976;Kaneko et ah, 1985].…”

Comparison of the effects of hypertonic glycerol and urea on brain edema, energy metabolism and blood flow following cerebral microembolism in the rat. Deleterious effect of glycerol treatment.

“…4 The mean radioactivity present in one microsphere was determined by simultaneous counting of the microsphere suspension in a hemocytometer and a scintillation crystal well counter in order to calculate the number of microspheres contained in the cerebral hemispheres.…”

“…Among the hyperosmolar agents, glycerol attracted more attention than the other substances because in addition to its osmotic activity it can be metabolized by brain. 2 " 4 Numerous experimental works [5][6][7][8][9][10][11][12][13] have reported the effect of glycerol or urea on brain water and electrolytes or on intracranial pressure but little is known about their actions on cerebral circulation and metabolism of the ischemic brain. The aim of the present study was to assess the effect of glycerol on brain edema, cerebral blood flow and metabolism compared to an equivalent dose of the metabolically inert urea.…”

Glycerol oxidation in discrete areas of rat brain from young, adolescent, and adult rats

“…In whole brain the rate of glycerol oxidation increased during the second to third week of life to levels comparable to those found in adults. Earlier work by our group (Tildon et al, 1976) and others (Goodner et al, 1973) suggested that the rate of glycerol oxidation in adult rat brain was higher in hypothalamus than in cortex. A high rate of glycerol oxidation may reflect the importance of glycerol as an energy substrate in that area of brain.…”