On the origin of mitochondria: a reexamination of the molecular structure and kinetic properties of pyruvate dehydrogenase complex from brewer''s yeast

45Ca2+ incorporated in response to glucose was selectively mobilized from the beta-cell-rich pancreatic islets of ob/ob-mice after raising the intracellular Na+ by removal of K+ or addition of ouabain or veratridine. Also studies of insulin release indicated opposite effects of glucose and Na+ on the intracellular sequestration of calcium. The fact that glucose inhibits insulin release induced by raised intracellular Na+ indicates that this sugar can lower the cytoplasmic [Ca2+]. The concept of a dual action of glucose on the cytoplasmic [Ca2+]. The concept of a dual action of glucose on the cytoplasmic [Ca2+] might well explain previous observations of an inhibitory component in the glucose action on the 45Ca2+ efflux.     

ATP synthesis in lettuce seeds during ripening

During the ripening of lettuce seeds, ATP, AMP + ADP, and moisture decrease to very low levels, and the ability to produce ATP from AMP + PEP (phosphoenolpyruvate) and the PEP-carboxylase (EC 4.1.1.38) activity is diminished. Malate dehydrogenase (EC 1.1.1.37) and pyruvate kinase (PK) (EC 2.7.1.40) decreased up to 10 days after anthesis, after which a sharp increase occurred.     

Influx of γ-Aminobutyric Acid and α-Aminoisobutyric Acid into Mouse Cerebrum Slices Incubated in a Pyruvate Medium with or without Added Glucose or Glucose Analogues Compared with Influx from a Glucose Medium

Concentrative influx of γ-aminobutyric acid (GABA) and α-aminoisobutyric acid (AIB) into incubated mouse cerebrum slices is decreased when pyruvate is substituted for glucose. Influx of GABA from pyruvate medium is not increased by presence of glucose, 2-deoxy-d -glucose (2-DOG), or 3-O-methyl-d -glucose (3-O-MeG). Influx of AIB is restored to the rate from glucose medium if 2-DOG is present initially, but is not restored if 2-DOG is added with AIB. Influx is not restored if 3-O-MeG is present initially, but is restored if 3-O-MeG is added with AIB. Influx is restored if glucose is present initially or is added with AIB.     

An allele (Pk-1 b ) from wild-caught mice that affects the activity and kinetics of erythrocyte and liver pyruvate kinase

A true breeding strain was made from a wild-caught mouse with low erythrocyte pyruvate kinase (E.C. 2.7.1.40) activity. This variation showed additive inheritance and segregated as an allele at a single locus (Pk-1 ^b). Mice homozygous for the reduced blood pyruvate kinase activity cosegregated for reduced liver activity. In both these tissues the variant enzyme had a lowered heat stability and reduced K _m values for ADP. An increased stimulation by FDP was also detected in the liver pyruvate kinase. No difference in the isoelectric point of the variant enzyme in either erythrocyte or liver was observed when compared with the enzyme from C57BL mice (Pk-1 ^a/Pk-1 ^a). It is concluded that Pk-1 is the structural gene for the erythrocyte and the major liver pyruvate kinase. No other tissue pyruvate kinase showed altered characteristics.This work was supported by a Medical Research Council grant.     

Regulatory properties of a partially purified preparation of pyruvate kinase from Fasciola hepatica

It possesses sigmoid kinetics with PEP; FBP activation changes the relationship to a rectangular hyperbola. The enzyme is inhibited by malate, which competes with PEP; FBP relieves the inhibition slightly. ATP and bicarbonate ions are also inhibitory at high concentrations. ATP inhibition is mixed-competitive with PEP; bicarbonate inhibition is non-competitive. It is suggested that pyruvate kinase may regulate both lactate and acetate production by moderating the size of the cytosolic pyruvate pool.     

Evidence for two genetic complementation groups in pyruvate carboxylase-deficient human fibroblast cell lines

We have examined genetic complementation in pyruvate carboxylase deficiency by comparing the enzyme activity in polyethylene glycol-induced heterokaryons with that in unfused mixtures of fibroblasts from three affected children. Complementation, manifested as a three- to sevenfold increase in pyruvate carboxylase activity, was observed in fusions between a biotin-responsive multiple carboxylase (pyruvate carboxylase, propionyl CoA carboxylase, and -methylcrotonyl CoA carboxylase) deficient fibroblast line and two other lines deficient only in pyruvate carboxylase activity. Kinetic analysis of complementing pyruvate carboxylase deficient lines, measured by the rate of restoration of enzyme activity as a function of time, revealed that maximum restoration was achieved within 10–24 hr after fusion. This profile is similar to those observed for fusions between the multiple carboxylase deficient line and two lines deficient in propionyl CoA carboxylase activity that are known to represent different gene mutations. Although the patients with pyruvate carboxylase deficiency had similar clinical findings, our studies indicate that pyruvate carboxylase deficiency is genetically heterogeneous, with at least two distinct, probably intergenic, complementation groups.This work was supported by an NIH research grant (AM 25675) and an A. D. Williams research grant (6-48360). B. Wolf is the recipient of an NIH Research Career Development Award (AM 00677) and is aided by a Basil O'Connor Starter Research Grant from The National Foundation-March of Dimes (5-263). G. Feldman is the recipient of an NIH predoctoral training grant (GM 07492). This article is No. 100 from the Department of Human Genetics at the Medical College of Virginia.     

A novel reaction of S-adenosyl-L-methionine correlated with the activation of pyruvate formate-lyase

Conversion of the inactive form of pyruvate formate-lyase to the catalytically active enzyme is accomplished by the Fe-dependent ‘enzyme II’; reduced flavodoxin, S-adenosyl-L-methionine and the effector pyruvate are required. It was found that adenosylmethionine is reductively processed during activation of pyruvate formate-lyase to yield methionine, adenine and 5-deoxyribose. We suggest that transient adenosylation of enzyme II is required for its function as a converter enzyme.     

A study on the potential reprotoxic effects of thimerosal in male albino rats

Thimerosal is ethyl mercury based compound which is being used as a preservative in vaccines since decades. Pharmaceutical products and vaccines that contain thimerosal are among the potential source of mercury exposure. Current research was intended to ascertain the reprotoxic effects of thimerosal on rat testes. Twenty-four adult male albino rats were sorted into four groups (n = 6). The first group was a control group. Rats of experimental Group 2, 3 and 4 were treated with various dosages of thimerosal (0.5, 10, 50 mg/kg) respectively. Rats were decapitated after thirty days of trial and different parameters were analyzed. Thimerosal exposure resulted in a significant decrease in antioxidant enzyme activities including catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), glutathione reductase (GSR) and increased levels of thiobarbituric acid reactive substances (TBARS). Different doses of thimerosal significantly decreased (p < 0.05) the concentration of plasma testosterone, luteinizing hormone (LH) and follicle stimulating hormone (FSH). Additionally, Daily sperm production (DSP) and efficiency of daily sperm production were significantly reduced followed by thimerosal exposure. Moreover, thimerosal significantly (p < 0.05) decreased the primary spermatocytes, secondary spermatocytes, number of spermatogonia along with spermatids. Thimerosal induced adverse histopathological and morphological changes in testicular tissues such as decreased Leydig cells, diameter of seminiferous tubules, tunica albuginea height and epithelial height. On the other hand, the increase in tubular lumen and interstitial spaces was observed due to thimerosal. These outcomes indicated that thimerosal has potential reprotoxic effects in male albino rats.