CoA-transferase Activity Research Articles

Effect of phenylalanine metabolites on the activities of enzymes of ketone-body utilization in brain of suckling rats.

1. The effects of phenylalanine and its metabolites (phenylacetate, phenethylamine, phenyl-lactate, o-hydroxyphenylacetate and phenylpyruvate) on the activity of 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) 3-oxo acid CoA-transferase (EC 2.8.3.5) and acetoacetyl-CoA thiolase (EC 2.3.1.9) in brain of suckling rats were investigated. 2. The 3-hydroxybutyrate dehydrogenase from the brain of suckling rats had a Km for 3-hydroxybutyrate of 1.2 mM. Phenylpyruvate, phenylacetate and o-hydroxyphenylacetate inhibited the enzyme activity with Ki values of 0.5, 1.3 and 4.7 mM respectively. 3. The suckling-rat brain 3-oxo acid CoA-transferase activity had a Km for acetoacetate of 0.665 mM and for succinyl (3-carboxypropionyl)-CoA of 0.038 mM. The enzyme was inhibited with respect to acetoacetate by phenylpyruvate (Ki equals 1.3 mM) and o-hydroxyphenylacetate (Ki equals 4.5 mM). The reaction in the direction of acetoacetate was also inhibited by phenylpyruvate (Ki equals 1.6 mM) and o-hydroxyphenylacetate (Ki equals 4.5 mM). 4. Phenylpyruvate inhibited with respect to acetoacetyl-CoA both the mitochondrial (Ki equals 3.2 mM) and cytoplasmic (Ki equals 5.2 mM) acetoacetyl-CoA thiolase activities. 5. The results suggest that inhibition of 3-hydroxybutyrate dehydrogenase and 3-oxo acid CoA-transferase activities may impair ketone-body utilization and hence lipid synthesis in the developing brain. This suggestion is discussed with reference to the pathogenesis of mental retardation in phenylketonuria.

Succinyl-CoA: 3-ketoacid CoA-transferase deficiency. A cause for ketoacidosis in infancy.

To explain the cause of a unique form of severe and intermittent ketoacidosis in an infant who expired after 6 months of life, tissue culture fibroblasts and post mortem tissue were examined for enzyme activities that catalyze glucose and ketoacid oxidation. No measurable succinyl-CoA: 3-ketoacid CoA-transferase (CoA-transferase) activity could be detected in homogenates of the post mortem brain, muscle and kidney tissue, or in the cultured skin fibroblasts. Since seven other enzyme activities involving both glycolysis and ketone body oxidation were present in these same tissues, it was reasonable to conclude that the observed absence of CoA-transferase activity was not an artifact of homogenate preparation. It was concluded that the absence of CoA-transferase activity resulted in a loss of intracellular homeostasis leading to ketoacidosis. In addition, the absence of this enzyme appears to be a reasonable explanation for the alteration in glucose metabolism that was previously reported in fibroblasts from this patient.

CoA transferase in the brain and other mammalian tissues

Succinyl-CoA: 3-ketoacid CoA-transferase (EC 2.8.3.5) activity was demonstrated in the brain of man, rat, mouse, guinea pig, and pigeon, but not of the dog, calf, and pig. In contrast to the enzyme from heart tissue, the brain enzyme was a particulate protein which sedimented with the mitochondrial fraction. The protein could be solubilized in 0.3% deoxycholate, or by freezing and thawing, and fractional salt and acid precipitation, and DEAE-cellulose chromatography yielded a 300-fold purification of the rat brain enzyme. Double reciprocal plots of one substrate vs velocity at several concentrations of the second substrate resulted in parallel lines which suggested a “ping-pong” mechanism as has been described for the pig heart enzyme. The K m values for succinate, acetoacetate, and succinyl CoA were 3.9 × 10 −2, 2.9 × 10 −4, and 6.7 × 10 −4 m, respectively. In the rat, the thermal lability, acrylamide gel electrophoretic mobility, and substrate specificity were essentially the same for the enzymes obtained from either heart, brain, or kidney. These findings support the suggested physiological role for the enzyme in ketone oxidation in central nervous tissue.

Mutations enabling Escherichia coli to grow on medium chain fatty acids

New spontaneous mutants of Escherichia coli able to use butyrate or valerate as carbon source have been studied for their growth, adaptation lag and the level of enzymes which may participate in the utilisation of these compounds.Each mutant acquires the simultaneous constitutivity for uptake of these fatty acids, CoA transferase and high thiolase activities. This mutation designated as butR does not affect the regulation of the β‐oxidation nor that of the glyoxylate cycle.Induction or mutation for constitutivity (oleR) of β‐oxidation act multiplicatively on the level of thiolase derepressed by the butR mutation.If the presence of CoA transferase, thiolase and C4–C5 fatty acids entry system is a prerequisite of the growth ability on these fatty acids, the genetic constitutivities (and not the preinduction) of the β‐oxidation (oleR) and particularly of the glyoxylic cycle (aceD) greatly increase the growth capacity. This implies that not only the C, and C, fatty acyl derivatives are very poor inducers of β‐oxidation, as already reported by others, but that some products of their catabolism repress the glyoxylic cycle.The acquisition of the new growth capacity is thus accomplished by spontaneous mutations affecting regulatory processes; one of these discloses activities which are cryptic in the normal parental strains; the physiological significance of these enzymatic potentialities in wild strains and the mechanism of the interaction between two different regulatory units brought to light here are some of the open issues.

Ketone Body Enzymes in Mammalian Tissues: EFFECT OF HIGH FAT DIET

Abstract Acetoacetyl coenzyme A thiolase activity of rat liver and 3-oxo acid CoA transferase activity of rat kidney were increased by 77% and 45%, respectively, after a diet containing 45% fat was given ad libitum for 1 week. No increase in activity of these two enzymes was noted in brain, not even after the rats were on the diet for 2 weeks. The data suggest that the ability of the adult rat brain to utilize ketone bodies does not depend on the nutritional state of the rat.

Succinyl-CoA: 3-Ketoacid-CoA transferase (CoA transferase) deficiency, a new cause of keto-acidosis in infancy

In an infant with a unique form of persistent ketonemia and severe intermittent keto-acidosis, studies of post mortem brain, muscle and kidney tissue demonstrated the absence of CoA transferase, a critical enzyme in ketone metabolism. Other enzymes of glucose and ketone metabolism were present in both post mortem tissues and skin fibroblasts from this patient. The tissue culture fibroblasts in addition to having no CoA transferase activity, demonstrated an altered carbohydrate metabolism compared to that of normal cells. When initially harvested, these cells utilized glucose at a rate significantly less than that of controls (125 vs 680 mμM/mg/hr). However, after incubation of 2.5 mM glucose for 18 hours, glucose uptake by patient's cell increased 20 fold (2560 mμM/mg/hr) whereas, that by control cells remained constant (680 ± 90). Concomitant with this increase, glucose-6-14C oxidation to 14CO2 in patient's fibroblasts rose from 8 to 2261 μμM/mg/hr, while that in control cells remained constant (485 ± 175). This increase in glucose utilization was not due to new enzyme formation since incubation with puromycin had no effect. Mixing experiments demonstrated no transfer of permeable inhibitors or activating substances. These data indicate that the absence of CoA transferase was the probable cause of the keto-acidosis in this infant and of the abnormal glucose metabolism in the fibroblasts suggesting a regulatory role for this enzyme in peripheral tissue glycolysis.