Effects of Ca2+ and Mg2+ on motility of sea urchin spermatozoa

Summary Swimming speed of sea urchin spermatozoa, measured by a light scattering technique, did not change with 0-20 mM Ca²⁺ in the medium. The speed was maximum at the normal concentration of Mg²⁺ (49 mM) in sea water.Supported by grants-in-aid from the Ministry of Education, Science and Culture, Japan, and a grant from the Ford Foundation.     

Epithelial localization of pyruvate kinase L (ATP pyruvate phosphotransferase EC 2.7.1.40) in rat liver]

Using three methods: histoenzymatic and immunoenzymatic, stained with tetrazolium salt, and immunofluorescence, we have localized PK "L" in hepatocytes. This localization in the cytoplasm of the cells differs widely in intensity with diet or hormone administration. Maximal with animals fed on high carbohydrate diet, still elevated with a subsequent insulin administration, it decreases with a normal diet to become weaker in animals, which have fasted for 48 hrs.     

The development of pyruvate kinase,glycerol kinase and phosphoenolpyruvate carboxykinase activities in liver and adipose tissue of the rat

Zusammenfassung Es wird gezeigt, dass in der Leber die Aktivität der PEP-Kinase und der Glycerolkinase nachgeburtlich ansteigt. Im braunen Fettgewebe fällt die PEP-Kinaseaktivität nach dem 40. Tag ab. Sie fehlt im weissen Fettgewebe. Die Pyruvatkinaseaktivität fällt in der Leber nach der Geburt ab, während sie im braunen Fettgewebe ansteigt.     

Phosphorylation of human red cell and liver pyruvate kinase. Differences between liver and erythrocyte L-type subunits

Summary Purified PK from human erythrocyte was phosphorylated by cAMP-dependent protein kinase type I from human erythrocyte membrane; this phosphorylation affected only the heavy L subunit but not the L subunit. On the other hand, the L subunit of liver PK was highly phosphorylated. Thus it appears that the L subunits from erythrocyte and liver PK are not identical protein molecules.Acknowledgments. This work was supported by a grant from INSERM (ATP 52.77.84). We thank J. Marie and Dr A. Kahn for the gift of purified liver PK.     

Inhibition of liver fructose 1,6-bisphosphatase activity by Zn2+: Reversal by imidazole pyruvate

Summary Imidazole pyruvate was found to be a very potent natural chelating agent in reversing the inhibition of liver fructose 1,6-bisphosphatase activity by Zn²⁺. This metabolite may play a physiological role in gluconeogenesis.This work was supported by grant RR-8006 from the General Research Branch, Division of Research Resources, NIH, USA.     

Extracellular Ca2+ and Mg2+ and cellular metabolism of phospholipids.

High extracellular concentration of Ca2+ inhibits the incorporation of 32P into the cellular phospholipids. This effect is more significant in neoplastic than in normal cells, and it is accompanied by an increase of the percentual incorporation into the lecithin fraction.     

Extracellular Mg2+ regulates intracellular Mg2+ and its subcellular compartmentation in fission yeast, Schizosaccharomyces pombe

Effects of extracellular magnesium ions ([Mg²⁺]_o ) on intracellular free Mg²⁺ ([Mg²⁺]_i ) and its subcellular distribution in single fission yeast cells, Schizosaccharomyces pombe, were studied with digital-imaging microscopy and an Mg²⁺ fluorescent probe (mag-fura-2). Using 0.44 mM [Mg²⁺]_o , [Mg²⁺]_i in yeast cells was 0.91±0.08 mM. Elevation of [Mg²⁺]_o to 1.97 mM induced rapid (within 5 min) increments in [Mg²⁺]_i (2.18±0.11 mM). Lowering [Mg²⁺]_o to 0.06 mM, however, exerted no significant effects on [Mg²⁺]_i (0.93±0.14 mM), at least for periods of up to 30 min. Irrespective of the [Mg²⁺]_o used, the subcellular distribution of [Mg²⁺]_i remained hetero geneous, i.e. where the sub-plasma membrane region >cytoplasm >nucleus. [Mg²⁺] in all three subcellular compartments increased significantly, two- to threefold, concomitant with [Mg²⁺]_i when placed in 1.97 mM [Mg²⁺]_o . We conclude that [Mg²⁺]_i in fission yeast is maintained at a physiologic level when [Mg²⁺]_o is low, but intracellular free Mg²⁺ rapidly rises when [Mg²⁺]_o is elevated. Like most eukaryotic cells, yeast may have a Mg²⁺ transport system(s) which functions to maintain gradients of Mg²⁺ from the outside to inside the cell and among its subcellular compartments. Received 18 April 1996; received after revision 4 July 1996; accepted 26 July 1996     

Response of briefly glycerinated smooth muscle to Ca2+ and Mg2+

Summary Smooth muscle, treated with 50% glycerol solution at 27°C for 20 min, contracted on the application of Ca²⁺ or Mg²⁺. The briefly glycerinated smooth muscle can be used as a model system of smooth muscle contraction.     

Inhibition of liver fructose 1,6-bisphosphatase activity by Zn2+: reversal by imidazole pyruvate.

Imidazole pyruvate was found to be a very potent natural chelating agent in reversing the inhibition of liver fructose 1,6-bisphosphatase activity by Zn2+. This metabolite may play a physiological role in gluconeogenesis.     

Effects of environmental changes on the incorporation of carbon atoms of pyruvate into mouse brain and liver

Résumé L'incorporation des atomes radioactifs de 1-¹⁴C-pyruvate dans le cerveau des souris est plus marquée quand les animaux ont soumis à un isolement prolongé.

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This study was supported by the United States Public Health Service (FVD) and by MH No. 15352 (RMP).     

Effects of increased intracellular Ca2+ on cyclic nucleotides production by liver tissue

Summary During hepatointoxication, the increase of intracellular Ca²⁺ is accompanied by an increase of cAMP. This reversible phenomenon suggests that the production of cAMP is likely to be a response of the cell in order to activate the exclusion of Ca²⁺.This work was supported by a grant from the Ministerium für Wissenschaft und Forschung des Landes Nordrhein-Westfalen.     

Mg2+-ATPase defective mutant ofEscherichia coli and thiamine transport

Summary Mg²⁺-ATPase deficient mutant ofEscherichia coli showed an evident dependency of thiamine uptake on the oxidative metabolism of glucose, whereas the parent strain did not. In both cells, this uptake was completely inhibited by H⁺ conductors.Acknowledgment. We are indebted to Miss M. Abe for her excellent technical assistance.     

Mn2+ electron spin resonance studies on ATP phosphoribosyltransferase fromE. coli

Summary ESR binding studies of Mn²⁺ with each of the substrates and products suggests that substrate bridge complexes are formed in the reaction. This prediction is confirmed, comparing Mn²⁺+ADP and Mn²⁺+ADP+enzyme spectra.We thank V. M. Fernández for helpful discussions.