Glycerol Phosphate Dehydrogenase, Glucose‐6‐Phosphate Dehydrogenase, and Lactate Dehydrogenase: Activities in Oligodendrocytes, Neurons, Astrocytes, and Myelin Isolated from Developing Rat Brains

Abstract

Glycerol phosphate dehydrogenase (GPDH), glucose-6-phosphate dehydrogenase (G6PDH), and lactate dehydrogenase (LDH) activities were determined in oligodendrocytes, neurons, and astrocytes isolated from the brains of developing rats. The activity of each enzyme was significantly lower in both neurons and astrocytes than in oligodendrocytes. The GPDH activity in oligodendrocytes increased more than 4-fold during development, and at 120 days cells of this type had 1.4-fold the specific activity of forebrain homogenates. The G6PDH activities in oligodendrocytes from 10-day-old rats were 1.4-fold the activities in the forebrain homogenates. The activities of this enzyme in oligodendrocytes were progressively lower at later ages, such that at 120 days the cells had 0.8 times the specific activities of homogenates. The oligodendrocytes had 0.6 times the homogenate activities of LDH at 10 days, and this ratio had decreased to 0.2 by 120 days. These enzymes were also measured in myelin isolated from 20-, 60-, and 120-day-old rats. By 120 days the specific activities of G6PDH and LDH in myelin were less than 8% of the respective activities in homogenates. The GPDH activity in myelin was, however, at least 20% the specific activity in the homogenates, even in the oldest animals. It is proposed that LDH could be used as a marker for oligodendroglial cytoplasm in subfractions of myelin and in myelin-related membrane vesicles.

Carbonic Anhydrase, 5′‐Nucleotidase, and 2′,3′‐Cyclic Nucleotide‐3′‐Phosphodiesterase Activities in Oligodendrocytes, Astrocytes, and Neurons Isolated from the Brains of Developing Rats

“…omitted from the reaction mixture, since it inhibited the activity in some samples used early in this study. The degree of contamination by erythrocytes in the cell preparations was estimated from the hemoglobin contents as described previously (Cammer et al, 1982). Erythrocytes contributed some of the carbonic anhydrase in only four of 24 preparations as follows: 21% in oligodendrocytes from 20-day-old rats; 2% in the oligodendrocytes from 60-day-old rats: 13% in neurons from Wday-old rats; and 21% in neurons from 120-day-old rats.…”

Phospholipid Biosynthesis in Myelin: Presence of CTP: Phosphoethanolamine Cytidylyltransferase in Purified Myelin of Rat Brain

“…Protein content was determined by the procedure of Lowry et al (1951). Lactate dehydrogenase was assayed by the procedure of Bernstein and Everse (1975), as described by Cammer and co-workers (Cammer et al, 1982;Cammer and Zimmerman, 1983). Decrease of NADH was first measured for 5-10 min in the absence of pyruvate (autoxidation); pyruvate was then added and NADH loss measured for 10 min at 340 nm for homogenate and soluble fractions and at 360 nm (with correction) for myelin.…”

Stimulation of H2O2 generation by calcium in brain mitochondria respiring on α‐glycerophosphate

“…Maechler et al (1997) claimed recently that mitochondrial α‐GPDH is a key component of the pancreatic β‐cell glucose sensing device, and mutations in the calcium‐binding domain of the enzyme have been detected in patients suffering from familial Type‐2 diabetes (Novials et al, 1997). The existence of the α‐GP shuttle in the brain has been shown in several studies (Cammer et al, 1982; McKenna et al, 1993; Atlante et al, 2001; Waagepetersen et al, 2001) and high rate of α‐GP oxidation has been found in brain mitochondria (Beleznai et al, 1988; Zoccarato et al, 1988; Tretter et al, 2007b).…”

“…α‐GPDH participates in the series of reactions called glycerophosphate shuttle (Klingenberg, 1970), necessary to transport glycolytic NADH into mitochondria. The role of the glycerophosphate shuttle in the brain is controversial, but numerous studies indicate that in neurons it is functional (Cammer et al, 1982; McKenna et al, 1993, 2006; Atlante et al, 1999; Waagepetersen et al, 2001). α‐GPDH is localized in the outer surface of the mitochondrial inner membrane (Donnellan et al, 1970; Klingenberg, 1970) and electrons derived from the oxidation of α‐GP to dihydroxyacetone phosphate are donated via FADH 2 to ubiquinone.…”