Metoprolol and mephenytoin oxidation polymorphisms in Far Eastern Oriental subjects: Japanese versus mainland Chinese

We examined genetically determined oxidation polymorphisms of metoprolol and mephenytoin in 200 unrelated, healthy Japanese subjects and in 98 mainland Chinese subjects simultaneously. This examination was done according to the respective reported phenotyping criteria by use of the urinary metabolic ratio of metoprolol and of the percentage of excretion of 4-hydroxymephenytoin 8 hours after dose administration. The frequencies of occurrence of poor metabolizers (PMs) in the Japanese versus the Chinese subjects were 0.5% versus 0% for metoprolol and 22.5% versus 17.4% for mephenytoin, respectively. There were no statistically significant differences in these frequencies between the two Oriental populations. However, Chinese extensive metabolizers (EMs) showed a significantly lower excretion of alpha-hydroxymetoprolol (p less than 0.01) and 4-hydroxymephenytoin (p less than 0.001) than that of Japanese EMs, and the mode of the distribution histogram of the Chinese EMs for the two test probes was skewed compared with that of the Japanese EMs. The findings indicate that the two Far Eastern Oriental subject groups have a lower frequency of PM phenotype of debrisoquin/sparteine-type oxidation and a greater incidence of PM phenotype of mephenytoin oxidation compared with the respective frequencies reported from white subjects. However, the explanation for the observation that the metabolic capacities of the test drugs differed between the EMs of the two populations who had a similar ethnic origin and who resided in the same geographic area remains obscure.

A previously undescribed plasmid and African R plasmid in Neisseria gonorrhoeae isolated in Taiwan

A new undescribed plasmid, 15.6-Mdal in size, was detected in Neisseria gonorrhoeae isolates in Taiwan. The plasmid was co-existent with 2.6-Mdal and 7.8-Mdal plasmids in three out of 190 clinical isolates. It appeared to be consisted of six copies of the 2.6-Mdal plasmids as evidenced by restriction endonuclease cleavage. In addition, African 3.2-Mdal R plasmids have also been detected in penicillinase-producing N. gonorrhoeae (PPNG) isolates in Taiwan. They accounted for 7% of PPNG.

Prolongation of G1 and S phase in C-6 glioma cells treated with maple syrup urine disease metabolits. Morphologic and cell cycle studies

Metabolites accumulating in maple syrup urine disease, a disease attributable to an inborn error in the catabolism of branched-chain amino acids, were administered to rat C-6 glioma cells maintained in monolayer culture in order to study the morphologic and cell kinetic changes caused by these metabolites. Computer analysis of fraction-labeled mitoses in combination with flow microfluorometric analysis was used to analyze the effects of these metabolites on the cell cycle. The maple syrup urine disease metabolites, i.e., L-leucine, L-isoleucine, and L-valine and their corresponding ketoacids caused a prolongation of the G1 and S phases, when administered in combination at concentrations corresponding to approximately the highest recorded plasma levels in patients with the disease (1 x level). This effect was not reversible. Ketoleucine (alpha-ketoisocarproic acid or AKICA) alone, the compound that accumulates in maple syrup urine disease and that has previously been shown to be the most important metabolite associated with it, caused marked prolongation of the G1 and, to a lesser extent, the S phase at concentrations of 200 mg. per 100 ml. Return of the AKICA-treated growth-arrested cells to a standard medium caused complete reversal of grwoth inhibition. Consistent fine structural changes were found in cells treated with AKICA at concentrations of 300 mg. per 100 ml. or with the combined maple syrup urine disease metabolites at a 2 x level. These included marked cell process elongation and the appearance of numerous bundles of cytoplasmic filaments.

Energy metabolism during brain ischemia. Stability during reversible and irreversible damage

The permissible duration of brain ischemia without sustaining damage is short. Less clear are the mechanisms accounting for the vulnerability of brain to ischemic insults. Neurochemical factors implicated include impairment of energy synthesis by mitochondria and of energy-dependent processes such as synaptic transmission, ATPase activity, membrane conductance and altered protein and lipid synthesis. To clarify the vulnerability of energy metabolism, we investigated energy availability and synthesis in our model of global cerebral ischemia. Our studies evaluated in vitro mitochondrial ATP synthesis and the in vivo quantitation of the cortical adenylate pool. Results of our investigations support a growing body of evidence showing the energy state to be relatively stable to ischemia. We conclude that an energy-dependent process of brain is primarily vulnerable to ischemia.

Regulation at the phosphoenolpyruvate branchpoint in Azotobacter vinelandii: pyruvate kinase

Pyruvate kinase (EC 2.7.1.40) from Azotobacter vinelandii responds sharply to the adenylate energy charge, with a decrease in activity at high values of charge, as expected for an enzyme of an adenosine triphosphate-regenerating sequence. Glycolytic intermediates, especially glucose 6-phosphate, fructose 6-phosphate, and fructose-1,6-diphosphate, strongly stimulate the reaction and overcome the inhibition caused by high values of energy charge. Thus, the properties of this enzyme depend on interaction between energy charge and the concentrations of hexose phosphates. The properties of pyruvate kinase, together with those of phosphoenolpyruvate carboxylase, aspartokinase, and citrate synthase, seem adapted to provide appropriate partitioning of phosphoenolpyruvate between competing pathways in response to metabolic need.

Regulation at the phosphoenolpyruvate branchpoint in Azotobacter vinelandii: phosphoenolpyruvate carboxylase

Phosphoenolpyruvate carboxylase (EC 4.1.1.31) from Azotobacter vinelandii, like the corresponding enzyme from other organisms, is activated by acetyl coenzyme A and inhibited by l-aspartate. Both modifiers affect primarily the affinity of the enzyme for phosphoenolpyruvate. This is the first enzyme with a strictly anaplerotic (intermediate-replacing) function to be tested for response to the adenylate energy charge; it is entirely insensitive to variation in charge. The results suggest that carboxylation of phosphoenolpyruvate in this organism is controlled by negative feedback from aspartate and by the stimulatory effect of acetyl coenzyme A. The adenylate energy charge may be expected to affect the rate of this reaction indirectly through its effects on the concentrations of acetyl coenzyme A and l-aspartate.