Pyruvate dehydrogenase phosphate (PDHb) phosphatase in brain: activity, properties, and subcellular localization

Normoxic resuscitation after cardiac arrest protects against hippocampal oxidative stress, metabolic dysfunction, and neuronal death

Resuscitation and prolonged ventilation using 100% oxygen after cardiac arrest is standard clinical practice despite evidence from animal models indicating that neurologic outcome is improved using normoxic compared with hyperoxic resuscitation. This study tested the hypothesis that normoxic ventilation during the first hour after cardiac arrest in dogs protects against prelethal oxidative stress to proteins, loss of the critical metabolic enzyme pyruvate dehydrogenase complex (PDHC), and minimizes subsequent neuronal death in the hippocampus. Anesthetized beagles underwent 10 mins ventricular fibrillation cardiac arrest, followed by defibrillation and ventilation with either 21% or 100% O2. At 1 h after resuscitation, the ventilator was adjusted to maintain normal blood gas levels in both groups. Brains were perfusion-fixed at 2 h reperfusion and used for immunohistochemical measurements of hippocampal nitrotyrosine, a product of protein oxidation, and the E1alpha subunit of PDHC. In hyperoxic dogs, PDHC immunostaining diminished by approximately 90% compared with sham-operated dogs, while staining in normoxic animals was not significantly different from nonischemic dogs. Protein nitration in the hippocampal neurons of hyperoxic animals was 2-3 times greater than either sham-operated or normoxic resuscitated animals at 2 h reperfusion. Stereologic quantification of neuronal death at 24 h reperfusion showed a 40% reduction using normoxic compared with hyperoxic resuscitation. These results indicate that postischemic hyperoxic ventilation promotes oxidative stress that exacerbates prelethal loss of pyruvate dehydrogenase and delayed hippocampal neuronal cell death. Moreover, these findings indicate the need for clinical trials comparing the effects of different ventilatory oxygen levels on neurologic outcome after cardiac arrest.

Brain regional development of the activity of alpha-ketoglutarate dehydrogenase complex in the rat

This study was initiated to test the hypothesis that the development of alpha-ketoglutarate dehydrogenase complex (KGDHC) activity, like that of pyruvate dehydrogenase complex, is one of the late developers of tricarboxylic acid (TCA) cycle enzymes. The postnatal development of KGDHC in rat brain exhibits four distinct region-specific patterns. The age-dependent increases in olfactory bulb (OB) and hypothalamus (HYP) form one pattern: low in postnatal days (P) 2 and 4, KGDHC activity rose linearly to attain adult level at P30. The increases in mid-brain (MB) and striatum (ST) constitute a second pattern: being <40% of adult level at P2 and P4, KGDHC activity rose steeply between P10 and P17 and attained adult level by P30. The increases in cerebellum (CB), cerebral cortex (CC), and hippocampus (HIP) form a third pattern: being 25-30% of adult level at P2 and P4, KGDHC activity doubled between P10 and P17 and rose to adult level by P30. KGDHC activity development is unique in pons and medulla (PM): being >60% of the adult level at P2, it rose rapidly to adult level by P10. Thus, KGDHC activity develops earlier in phylogenetically older regions (PM) than in phylogenetically younger regions (CB, CC, HIP). Being lowest in activity among all TCA cycle enzymes, KGDHC activity in any region at any age will exert a limit on the maximum TCA cycle flux therein. The results may have functional and pathophysiological implications in control of brain glucose oxidative metabolism, energy metabolism, and neurotransmitter syntheses.

Effect of nicardipine, a Ca2+ channel blocker, on pyruvate dehydrogenase activity and energy metabolites during cerebral ischemia and reperfusion in gerbil brain

The purpose of this study was to determine if nicardipine, a calcium ion channel blocker, affects pyruvate dehydrogenase (PDH) activity and improves energy metabolism during cerebral ischemia and reperfusion. Cerebral ischemia was induced, using the bilateral carotid artery occlusion method, for 60 min followed by reperfusion up to 120 min in gerbils. Nicardipine (1 mg/kg) or saline (vehicle-treated) was given to gerbils 30 min prior to the occlusion of the common carotid arteries. PDH activity and metabolites (ATP, PCr, and lactate) were measured in cortex prior to ischemia, immediately following ischemia, and after each reperfusion period. After 60 min ischemia, PDH activity increased in both groups, and was significantly higher in the nicardipine-treated group. After 20 min reperfusion, PDH activity in the nicardipine-treated group recovered to control levels, whereas, the PDH activity in the vehicle-treated group remained elevated, and was higher than the nicardipine-treated animals. At 60 and 120 min reperfusion, the activities in the vehicle-treated group were significantly below control levels, there were no differences, however, between the two groups. ATP and PCr concentrations were markedly depleted immediately after ischemia in both groups. ATP levels at 20 min reperfusion and PCr levels at 60 min reperfusion were significantly higher in the nicardipine-treated group. Lactate concentrations in both groups increased 7-8 fold, similarly, immediately after ischemia. During reperfusion, the lactate remained elevated in both groups, though the levels in the nicardipine-treated group were lower than those in the vehicle-treated group, but not significantly. Nicardipine treatment normalized PDH activity quickly and improved energy metabolism after reperfusion.

Decrease of pyruvate dehydrogenase phosphatase activity in patients with congenital lactic acidemia

We developed an assay method for pyruvate dehydrogenase phosphatase activity using [1-14C]pyruvate and measured pyruvate dehydrogenase phosphatase activity in cultured skin fibroblasts from three patients with congenital lactic acidemia due to a defect in activation of the pyruvate dehydrogenase complex. The enzyme activity of their fibroblasts was significantly reduced to 50.7%, 64.6% and 63.1% of that of control fibroblasts. These observations suggest that the defect in activation of the pyruvate dehydrogenase complex in these patients might be due to a reduction in pyruvate dehydrogenase phosphatase activity.

Changes in pyruvate dehydrogenase complex activity during and following severe insulin-induced hypoglycemia

The effect of severe insulin-induced hypoglycemia on the activity of the pyruvate dehydrogenase enzyme complex (PDHC) was investigated in homogenates of frozen rat cerebral cortex during burst suppression EEG, after 10, 30, and 60 min of isoelectric EEG, and after 30 and 180 min and 24 h of recovery following 30 min of hypoglycemic coma. Changes in PDHC activity were correlated to levels of labile organic phosphates and glycolytic metabolites. In cortex from control animals, the rate of [1-14C]pyruvate decarboxylation was 7.1 +/- 1.3 U/mg of protein, or 35% of the total PDHC activity. The activity was unchanged during burst suppression EEG whereas the active fraction increased to 81-87% during hypoglycemic coma. Thirty minutes after glucose-induced recovery, the PDHC activity had decreased by 33% compared to control levels, and remained significantly depressed after 3 h of recovery. This decrease in activity was not due to a decrease in the total PDHC activity. At 24 h of recovery, PDHC activity had returned to control levels. We conclude that the activation of PDHC during hypoglycemic coma is probably the result of an increased PDH phosphatase activity following depolarization and calcium influx, and allosteric inhibition of PDH kinase due to increased ADP/ATP ratio. The depression of PDHC activity following hypoglycemic coma is probably due to an increased phosphorylation of the enzyme, as a consequence of an imbalance between PDH phosphatase and kinase activities. Since some reduction of the ATP/ADP ratio persisted and since the lactate/pyruvate ratio had normalized by 3 h of recovery, the depression of PDHC most likely reflects a decrease in PDH phosphatase activity, probably due to a decrease in intramitochondrial Ca2+.

Thiamine-dependent enzyme changes in temporal cortex of patients with Alzheimer's disease

Activities of thiamine-dependent enzymes [pyruvate dehydrogenase (PDHC), alpha-ketoglutarate dehydrogenase (alpha KGDH), and transketolase (TK)] were measured in autopsied samples of temporal cortex from six patients with Alzheimer's disease and from eight age-matched control subjects who were free from neurological or psychiatric diseases. Times from death to freezing of dissected material at -70 degrees C were matched. Significant decreases in PDHC (decreased by 70%; P less than 0.01), alpha KGDH (decreased by 70%; p less than 0.01), and TK (decreased by 52%; P less than 0.01) were observed in brain tissue from patients with Alzheimer's disease. In contrast, activities of glutamate dehydrogenase were within normal limits. These findings suggest a possible role for alterations of brain thiamine metabolism or utilization in Alzheimer's disease.

Preischemic hyperglycemia and postischemic alteration of rat brain pyruvate dehydrogenase activity

Transient cerebral ischemia in normoglycemic animals is followed by a decrease in glucose utilization, reflecting a postischemic cerebral metabolic depression and a reduction in the activity of the pyruvate dehydrogenase complex (PDHC). Preischemic hyperglycemia, which aggravates ischemic brain damage and invariably causes seizure, is known to further reduce cerebral metabolic rate. To investigate whether these effects are accompanied by changes in PDHC activity, the postischemic cerebral cortical activity of this enzyme was investigated in rats with preischemic hyperglycemia (plasma glucose 20-25 mM). The results were compared with those obtained in normoglycemic animals (plasma glucose 5-10 mM). The activated portion of PDHC and total PDHC activity were measured in neocortical samples as the rate of decarboxylation of [14C]pyruvate in crude brain mitochondrial homogenates after 5 min, 15 min, 1 h, 6 h, and 18 h of recirculation following 15 min of incomplete cerebral ischemia. In normoglycemic animals the fraction of activated PDHC, which rises abruptly during ischemia, was reduced to 19-25% during recirculation compared with 30% in sham-operated controls. In hyperglycemic rats the fraction of activated PDHC was higher during the first 15 min of recirculation. However, after 1 and 6 h of recirculation, the fraction was reduced to values similar to those measured in normoglycemic animals. Fifteen of 26 rats experienced early (1-4 h post ischemia) seizures in the recovery period. The PDHC activity appeared unchanged prior to these early postischemic seizures. We conclude that the accentuated depression of postischemic metabolic rate observed in hyperglycemic animals is not coupled to a corresponding postischemic depression of PDHC.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural localization of choline acetyltransferase in the rat rostral ventrolateral medulla: evidence for major synaptic relations with non-catecholaminergic neurons

Pharmacological and biochemical studies suggest that interactions between cholinergic and catecholaminergic and catecholaminergic neurons, particularly those of the C1 adrenergic cell group, in the rostral ventrolateral medulla (RVL) may be important in cardiovascular control. Ultrastructural localization of choline acetyltransferase (ChAT), the biosynthetic enzyme for acetylcholine, and its relation to neurons exhibiting immunoreactivity for catecholamine- (tyrosine hydroxylase; TH) or adrenaline (phenylethanolamine-N-methyltransferase; PNMT) -synthesizing enzymes were examined in the RVL using dual immunoautoradiographic and peroxidase anti-peroxidase (PAP) labeling methods. By light microscopy, the ChAT-immunoreactive neurons were located both dorsally (i.e. the nucleus ambiguus) and ventromedially to those labeled with TH or PNMT (TH/PNMT). A few ChAT-labeled processes were dispersed among TH/PNMT-containing neurons with the majority of overlap immediately ventral to the nucleus ambiguus. By electron microscopy, ChAT-immunoreactivity (ChAT-I) was detected in neuronal perikarya, dendrites, axons and axon terminals and in the vascular endothelial cells of certain blood vessels. The ChAT-labeled perikarya in the ventromedial RVL were medium-sized (15-20 microns), elongated, contained abundant cytoplasm and had had slightly indented nuclei. Synaptic junctions on ChAT-immunoreactive perikarya and dendrites were primarily symmetric with 64% (45 out of 70) of the presynaptic terminals unlabeled. The remaining terminals were immunoreactive for ChAT (30%) or TH/PNMT (6%). Terminals with ChAT-I were large (0.8-2.0 microns) and contained numerous small clear vesicles and 1-2 dense core vesicles. Seventy-seven percent (112 out of 145) of the ChAT-labeled terminals formed symmetric synapses with unlabeled perikarya and dendrites, whereas only 8% were with TH/PNMT-labeled perikarya and dendrites, and 15% were with ChAT-immunoreactive perikarya and dendrites. We conclude (1) that cholinergic neurons in the RVL principally terminate on and receive input from non-catecholaminergic neurons, and (2) that the reported sympathetic activation following application of cholinergic agents to the RVL may be mediated by cholinergic inhibition of local inhibitory interneurons. The observed synapses between ChAT and TH/PNMT-containing neurons suggests that cholinergic and adrenergic neurons additionally may exert a minor reciprocal control on each other and thus may modulate their response to the more abundant input from afferents containing other transmitters.

Pyruvate dehydrogenase activity in the rat cerebral cortex following cerebral ischemia

The effect of cerebral ischemia on the activity of pyruvate dehydrogenase (PDH) enzyme complex (PDHC) was investigated in homogenates of frozen rat cerebral cortex following 15 min of bilateral common carotid occlusion ischemia and following 15 min, 60 min, and 6 h of recirculation after 15 min of ischemia. In frozen cortical tissue from the same animals, the levels of labile phosphate compounds, glucose, glycogen, lactate, and pyruvate was determined. In cortex from control animals, the rate of [1(-14)C]pyruvate decarboxylation was 9.6 +/- 0.5 nmol CO2/(min-mg protein) or 40% of the total PDHC activity. This fraction increased to 89% at the end of 15 min of ischemia. At 15 min of recirculation following 15 min of ischemia, the PDHC activity decreased to 50% of control levels and was depressed for up to 6 h post ischemia. This decrease in activity was not due to a decrease in total PDHC activity. Apart from a reduction in ATP levels, the acute changes in the levels of energy metabolites were essentially normalized at 6 h of recovery. Dichloroacetate (DCA), an inhibitor of PDH kinase, given to rats at 250 mg/kg i.p. four times over 2 h, significantly decreased blood glucose levels from 7.4 +/- 0.6 to 5.1 +/- 0.3 mmol/L and fully activated PDHC. In animals in which the plasma glucose level was maintained at control levels of 8.3 +/- 0.5 mumol/g by intravenous infusion of glucose, the active portion of PDHC increased to 95 +/- 4%. In contrast, the depressed PDHC activity at 15 min following ischemia was not affected by the DCA treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of 2-oxoglutarate or 3-hydroxybutyrate on pyruvate dehydrogenase complex in isolated cerebrocortical mitochondria

The oxidation of pyruvate is mediated by the pyruvate dehydrogenase complex (PDHC; EC 1.2.4.1, EC 2.3.1.12 and EC 1.6.4.3) whose catalytic activity is influenced by phosphorylation and by product inhibition. 2-Oxoglutarate and 3-hydroxybutyrate are readily utilized by brain mitochondria and inhibit pyruvate oxidation. To further elucidate the regulatory behavior of brain PDHC, the effects of 2-oxoglutarate and 3-hydroxybutyrate on the flux of PDHC (as determined by [1-14C]pyruvate decarboxylation) and the activation (phosphorylation) state of PDHC were determined in isolated, non-synaptic cerebro-cortical mitochondria in the presence or absence of added adenine nucleotides (ADP or ATP). [1-14C]Pyruvate decarboxylation by these mitochondria is consistently depressed by either 3-hydroxybutyrate or 2-oxoglutarate in the presence of ADP when mitochondrial respiration is stimulated. In the presence of exogenous ADP, 3-hydroxybutyrate inhibits pyruvate oxidation mainly through the phosphorylation of PDHC, since the reduction of the PDHC flux parallels the depression of PDHC activation state under these conditions. On the other hand, in addition to the phosphorylation of PDHC, 2-oxoglutarate may also regulate pyruvate oxidation by product inhibition of PDHC in the presence of 0.5 mM pyruvate plus ADP or 5 mM pyruvate alone. This conclusion is based upon the observation that 2-oxoglutarate inhibits [1-14C]pyruvate decarboxylation to a much greater extent than that predicted from the PDHC activation state (i.e. catalytic capacity) alone. In conjunction with the results from our previous study (Lai, J. C. K. and Sheu, K.-F. R. (1985) J. Neurochem. 45, 1861-1868), the data of the present study are consistent with the notion that the relative importance of the various mechanisms that regulate brain and peripheral tissue PDHCs shows interesting differences.

Pigeon liver phosphoprotein phosphatase: an effective activator of pyruvate dehydrogenase in tissue homogenates

A fluoride-insensitive, non-metal-requiring pyruvate dehydrogenase phosphatase has been purified 730-fold from pigeon liver acetone powder and proven to be a convenient reagent for studies of pyruvate dehydrogenase complex and its activation (phosphorylation) state in brain and other tissues. This phosphatase is a cytoplasmic enzyme (Mr = 80,000), and fits the functional definition of a type 1 phosphoprotein phosphatase. The pigeon liver phosphatase can be used to activate pyruvate dehydrogenase complex in vitro in brain and other crude tissue homogenates. Addition of the cytoplasmic pigeon liver phosphatase to a homogenate from rat or mouse brain frozen in situ activated pyruvate dehydrogenase to levels comparable to that found in ischemic brain. The fluoride insensitivity of this phosphatase was used to develop a convenient technique for stopping the pyruvate dehydrogenase activation state in situ in cultured skin fibroblasts and then fully activating the complex in vitro in 5 min. The use of this phosphatase as a reagent can facilitate the study of pyruvate dehydrogenase activation defects in mammalian tissues including cultured cells in normal and disease states.

Relationship between activation state of pyruvate dehydrogenase complex and rate of pyruvate oxidation in isolated cerebro-cortical mitochondria: effects of potassium ions and adenine nucleotides

The relation between the activation (phosphorylation) state of pyruvate dehydrogenase complex (PDHC; EC 1.2.4.1, EC 2.3.1.12, and EC 1.6.4.3) and the rate of pyruvate oxidation has been examined in isolated, metabolically active, and tightly coupled mitochondria from rat cerebral cortex. With pyruvate and malate as the substrates, the activation state of PDHC decreased on addition of ADP, while the rates of oxygen uptake and 14CO2 formation from [1-14C]pyruvate increased. The lack of correlation between the activation state of PDHC and rate of pyruvate oxidation was seen in media containing 5, 30, or 100 mM KCl. Both the activation state of PDHC and pyruvate oxidation increased, however, when KCl was increased from 5 to 100 mM. Although the PDHC is inactivated by an ATP-dependent kinase (EC 2.7.1.99), direct measurement of ATP and ADP failed to show a consistent relationship between the activation state of PDHC and either ATP levels or ATP/ADP ratios. Comparison of the activation state of PDHC in uncoupled or oligomycin-treated mitochondria also failed to correlate PDHC activation state to adenine nucleotides. In brain mitochondria, unlike those from other tissues, the activation state of PDHC does not seem to be related clearly to the rate of pyruvate oxidation, or to the mitochondrial adenylate energy charge.

Activities of thiamine-dependent enzymes in two experimental models of thiamine-deficiency encephalopathy: 1. The pyruvate dehydrogenase complex

Chronic thiamine deprivation in the rat leads to selective neuropathological damage in brainstem structures whereas treatment with the central thiamine antagonist, pyrithiamine, results in more widespread damage. In order to further elucidate the neurochemical mechanisms responsible for this selective damage, the thiamine-dependent enzyme complex pyruvate dehydrogenase (PDHC) was measured in 10 brain structures in the rat during progression of thiamine deficiency produced by chronic deprivation or by pyrithiamine treatment. Feeding of a thiamine-deficient diet to adult rats resulted in 5-7 weeks in ataxia and loss of righting reflex accompanied by decreased blood transketolase activities. PDHC activities were selectively decreased by 15-30% in midbrain and pons (lateral vestibular nucleus). Thiamine treatment of symptomatic rats led to reversal of neurological signs and to concomitant reductions of the cerebral PDHC abnormalities. Daily pyrithiamine treatment led within 3 weeks to loss of righting reflex and convulsions and to decreased blood transketolase of a comparable magnitude to that observed in chronic thiamine-deprived rats. No significant regional alterations of PDHC, however, were observed in pyrithiamine-treated rats.

Differences in some of the metabolic properties of mitochondria isolated from cerebral cortex and olfactory bulb of the rat

The metabolic properties of mitochondria from rat cerebral cortex and olfactory bulb were investigated. The pyruvate-supported oxygen uptake rates by olfactory bulb mitochondria were significantly lower than those by cerebrocortical mitochondria. This is consistent with the differences in pyruvate dehydrogenase complex activities between these mitochondrial preparations. Pyruvate dehydrogenase kinase, NAD-linked isocitrate dehydrogenase, and hexokinase activities in olfactory bulb mitochondria were significantly lower than those in cerebrocortical mitochondria. However, NADP-linked isocitrate dehydrogenase, and NAD-linked and NADP-linked glutamate dehydrogenase activities in olfactory bulb mitochondria were significantly higher than those in cerebrocortical mitochondria. The differences between these two mitochondrial preparations in terms of the activities of these energy-metabolizing enzymes reflect the differences detected in the homogenates of these regions.

An immunochemical study of the pyruvate dehydrogenase deficit in Alzheimer's disease brain

The activity of the pyruvate dehydrogenase complex (PDHC; EC 1.2.4.1, EC 2.3.1.12, and EC 1.6.4.3) was reduced to about 30% of control values in histologically unaffected occipital cortex of the brains of patients with Alzheimer's disease, as well as in histologically affected frontal cortex. In contrast, activity of another mitochondrial enzyme, glutamate dehydrogenase, was normal. Neither age nor time until postmortem study correlated significantly with PDHC activity in either Alzheimer or control samples, and PDHC was not inactivated significantly on incubation with homogenates of either Alzheimer or control brain. Antibodies against the highly purified bovine PDHC inhibited Alzheimer and control PDHC equally per unit of enzyme activity. Immunoblots also indicated that the PDHC antigens were not different in normal and Alzheimer brains. This antibody, however, inhibited Alzheimer PDHC more effectively than it did control PDHC, based on milligrams of protein, suggesting a reduced amount of normal PDHC protein. Other data suggest that the PDHC deficiency is related to mitochondrial damage and to impaired calcium homeostasis in Alzheimer nerve cells, which may then mediate a variety of other cellular impairments.

Immunochemical characterization of pyruvate dehydrogenase complex in rat brain

Pyruvate dehydrogenase complex (PDHC) in rat brain was studied immunochemically, using antibodies against the bovine kidney PDHC, by immunoblotting, immunoprecipitation, inhibition of enzyme activity, and enzyme-linked immunoabsorbent assay (ELISA). The immunoblots showed that the antibodies bound strongly to the alpha peptide of the pyruvate dehydrogenase (E1) component, and to the dihydrolipoyl transacetylase (E2) and the dihydrolipoyl dehydrogenase (E3) components of PDHC. A similar immunoblotting pattern was observed in all eight brain regions examined. On immunoblotting of the subcellular fractions, these PDHC peptides were observed in mitochondria and synaptosomes but not in the postmitochondrial supernatants. This agrees with other evidence that brain PDHC is localized in the mitochondria. These results, together with those from sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the immunoprecipitin, also showed that the alpha E1, beta E1, and E3 peptides of rat brain PDHC are very similar in sizes to those of the bovine kidney PDHC, being 42, 36, and 58 kD, respectively. The size of the E2 peptide, 66 kD, is different from that of bovine kidney E2, 73 kD. The relative abundance of PDHC protein in nonsynaptic mitochondria was compared by enzyme activity titration and ELISA. Both methods demonstrated that the amount of PDHC antigen in the mitochondria from cerebral cortex is greater than that in the olfactory bulb mitochondria. This is consistent with the results of the activity measurement. The ELISA also showed that the PDHCs in both mitochondrial populations are antigenically similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Depolarisation-dependent protein phosphorylation and dephosphorylation in rat cortical synaptosomes is modulated by calcium

The effect of calcium on protein phosphorylation was investigated using intact synaptosomes isolated from rat cerebral cortex and prelabelled with 32Pi. For nondepolarised synaptosomes a group of calcium-sensitive phosphoproteins were maximally labelled in the presence of 0.1 mM calcium. The phosphorylation of these proteins was slightly decreased in the presence of strontium and absent in the presence of barium, consistent with the decreased ability of these cations to activate calcium-stimulated protein kinases. Addition of calcium alone to synaptosomes prelabelled in its absence increased phosphorylation of a number of proteins. On depolarisation in the presence of calcium certain of the calcium-sensitive phosphoproteins were further increased in labelling above nondepolarised levels. These increases were maximal and most sustained after prelabelling at 0.1 mM calcium. On prolonged depolarisation at this calcium concentration a slow decrease in labelling was observed for most phosphoproteins, whereas a greater rate and extent of decrease occurred at higher calcium concentrations. At 2.5 mM calcium a rapid and then a subsequent slow dephosphorylation was observed, indicating two distinct phases of dephosphorylation. Of all the phosphoproteins normally stimulated by depolarisation, only phosphoprotein 59 did not exhibit the rapid phase of dephosphorylation at high calcium concentrations. Replacing calcium with strontium markedly decreased the extent of change observed on depolarisation whereas barium decreased phosphorylation changes even further. Taken together these data suggest that an influx of calcium into synaptosomes initially activates protein phosphorylation, but as the levels of intrasynaptosomal calcium rise protein dephosphorylation predominates. Other phosphoproteins were dephosphorylated immediately on depolarisation in the presence of calcium. The fine control of protein phosphorylation levels exerted by calcium supports the idea that the synaptosomal phosphoproteins could play a role in modulating events such as neurotransmitter release in the nerve terminal.

Studies on the bovine brain pyruvate dehydrogenase complex using the antibodies against kidney enzyme complex

Pyruvate dehydrogenase complex (PDHC) was purified from bovine kidney with a specific activity of 12-16 mumol of NADH or acetyl-CoA formed/min/mg protein. The four peptides comprising its three catalytic components were separated by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Rabbit antibodies against this highly purified PDHC (anti-PDHC) exhibited similar binding affinity to the phospho-PDHC as it did to the PDHC antigen. To test whether there exist brain isozymes of PDHC differing from kidney enzyme, which has been extensively characterized, the PDHCs in bovine brain and kidney were compared using this anti-PDHC. The PDHC activities in the brain and kidney mitochondrial extracts were inhibited to the same degree by varying amounts of anti-PDHC. Brain PDHC was precipitated with the anti-PDHC and resolved by SDS-PAGE. The four brain PDHC peptides isolated immunochemically with anti-PDHC had the same sizes as the kidney PDHC peptides. These PDHC peptides from kidney and brain were further compared by their peptide fragment patterns, which were generated by partial proteolysis with Staphylococcus aureus V8 protease or by CNBr and resolved by SDS-PAGE. The peptide patterns generated with the former method indicated that the alpha and beta peptides of the pyruvate dehydrogenase (E1) component and the peptide of dihydrolipoyl transacetylase (E2) component of kidney PDHC were very similar to the corresponding peptides immunologically isolated from brain. The peptide patterns generated with CNBr further confirmed that the beta E1 and E2 peptides of kidney PDHC were similar to the corresponding peptides from brain.

Pyruvate dehydrogenase activity in regions of the rat brain during postnatal development

Activity of the pyruvate dehydrogenase complex (PDHC) was measured in seven brain regions of the male rat at various times during the postnatal period using an arylamine acetyltransferase coupled assay. Three days after birth, PDHC activity was found to be less than 15% of adult values in all brain regions with the exception of hypothalamus and medulla-pons (30% of adult values in each case). Activity of the enzyme complex in these latter regions attained adult levels by 21 days postnatally, some 5-15 days ahead of that found in cerebral cortex, striatum, hippocampus, and cerebellum. Such differences in PDHC maturation reflect the greater degree of early maturity of the phylogenetically older brain structures. Cerebellar PDHC developed more slowly than in other brain regions to attain only 40% of adult levels by the time of weaning. The pattern of maturation of cerebellar PDHC is paralleled by increased incorporation of glucose into cerebral amino acids and by the pattern of development of parallel fiber synaptogenesis. These findings suggest that PDHC may play a key role in the regional development of metabolic compartmentation and the associated maturation of cerebral function in the rat.

Long-term potentiation in the hippocampal slice: possible involvement of pyruvate dehydrogenase

Tetanic stimulation of fibers in the hippocampal slice preparation produces long-term potentiation (LTP) and also decreases the in vitro incorporation of phosphate into the alpha subunit of pyruvate dehydrogenase (alpha PDH). This paper describes 6 experiments that were undertaken to replicate this observation. Hippocampal slices were incubated in a specially designed chamber and stimulated with a tungsten wire electrode in the stratum radiatum for 1 s at 100 Hz. Two minutes after the tetanus, the stimulated slices were removed alternately with control (not tetanized) slices and each group was pooled for subcellular fractionation and labeling of the fractions with [32P]ATP. Proteins were separated by electrophoresis and relative 32P contents of 41K and 50K protein bands were studied. Tetanic stimulation of the stratum radiatum did not affect subsequent phosphorylation of a 50K Mr protein that has been reported to be altered by perforant path activation. Stimulation also had no effect on pyruvate dehydrogenase enzyme activity or on the ratio of active (dephosphorylated) to inactive enzyme. In most cases tetanic stimulation produced no significant change in the in vitro phosphorylation of this enzyme. Only under one set of conditions, labeling with 250 microM [gamma-32P]ATP for 10 s, was a decrease in the in vitro labeling of alpha PDH shown to be statistically significant. These findings suggest that LTP is not necessarily accompanied by an initial change in PDH phosphorylation level or activity but may be associated with a decrease in the kinase activity directed toward this protein.

Correlation of enzymatic, metabolic, and behavioral deficits in thiamin deficiency and its reversal

To clarify the enzymatic mechanisms of brain damage in thiamin deficiency, glucose oxidation, acetylcholine synthesis, and the activities of the three major thiamin pyrophosphate (TPP) dependent brain enzymes were compared in untreated controls, in symptomatic pyrithiamin-induced thiamin-deficient rats, and in animals in which the symptoms had been reversed by treatment with thiamin. Although brain slices from symptomatic animals produced 14CO2 and 14C-acetylcholine from [U-14C]glucose at rates similar to controls under resting conditions, their K+-induced-increase declined by 50 and 75%, respectively. In brain homogenates from these same animals, the activities of two TPP-dependent enzymes transketolase (EC 2.2.1.1) and 2-oxoglutarate dehydrogenase complex (EC 1.2.4.2, EC 2.3.1.61, EC 1.6.4.3) decreased 60-65% and 36%, respectively. The activity of the third TPP-dependent enzyme, pyruvate dehydrogenase complex (EC 1.2.4.1, EC 2.3.1.12, EC 1.6.4.3) did not change nor did the activity of its activator pyruvate dehydrogenase phosphate phosphatase (EC 3.1.3.43). Although treatment with thiamin for seven days reversed the neurological symptoms and restored glucose oxidation, acetylcholine synthesis and 2-oxoglutarate dehydrogenase activity to normal, transketolase activity remained 30-32% lower than controls. The activities of other TPP-independent enzymes (hexokinase, phosphofructokinase, and glutamate dehydrogenase) were normal in both deficient and reversed animals.

Properties and regional distribution of pyruvate dehydrogenase kinase in rat brain

A method is described to measure directly in rat brain the activity of pyruvate dehydrogenase kinase (PDHa kinase; EC 2.7.1.99), which catalyzes the inactivation of pyruvate dehydrogenase complex (PDHC, EC 1.2.4.1, EC 2.3.1.12, and EC 1.6.4.3). The activity showed the expected dependence on added ATP and divalent cation, and the expected inhibition by dichloroacetate, pyruvate, and thiamin pyrophosphate. These results, and the properties of pyruvate dehydrogenase phosphate phosphatase (EC 3.1.3.43), indicate that the mechanisms of control of phosphorylation of PDHC seem qualitatively similar in brain to those in other tissues. Regionally, PDHa kinase is more active in cerebral cortex and hippocampus, and less active in hypothalamus, pons and medulla, and olfactory bulbs. Indeed, the PDHa kinase activity in olfactory bulbs is uniquely low, and is more sensitive to inhibition by pyruvate and dichloroacetate than that in the cerebral cortex. Thus, there are significant quantitative differences in the enzymatic apparatus for controlling PDHC activity in different parts of the brain.