Requirement For Mg2 Research Articles

The succinate-linked nicotinamide-adenine dinucleotide reduction in submitochondrial particles: I. Kinetic studies of the reaction

The succinate-linked NAD + reduction in sonic particles derived from beef-heart mitochondria has been described. The reaction showed an absolute requirement for Mg 2+. K m values for succinate, Mg 2+ and NAD + have been determined. A lag phase in NAD + reduction was observed which has been related to the link of energy and electron-transfer reactions. The pH optimum of the reaction was found to be at pH 8.5–9.0.

The Role of Magnesium in the Superprecipitation of Myosin B

In 1951 and 1952, Spicer (2-5) made a series of further studies on this phenomenon and described the “clearing” response, a phenomenon associated with the superprecipitation. The use of this model has been revived in recent studies (6-11) on the physiological function of “relaxing factors,” including ethylenediaminetetraacetate. In these studies, however, atten- tion has been focused on the role of Ca2+ in the superprecipita- tion in the presence of physiological (relatively ‘higher) concen- trations of Mg*, and the primary requirement of Mg*+ for superprecipitation has been somewhat overlooked. In the earlier studies, Szent-Gyorgyi (1) reported that addi- tion of Mg* in very low concentrations accelerated the process of superprecipitation. IMarugama and Tonomura (12), using crayfish myosin B, reported the inhibition of superprecipitation by ethylenediaminetetraacetate. However, no positive evidence has been reported that Mg*, but not Ca’+, is the primary re- quirement for the superprecipitation. In this paper, such posi- tive evidence for the Mg* requirement for superprecipitation will be presented.

Studies on acetocoenzyme a kinase from Euglena gracilis

The presence of acetoCoA kinase in Euglena gracilis has been established, and a ten-fold ourification achived. This enzyme has an absolute requirement for Mg 2+ ion, and its activity is optimum at pH 5.0. The K m value fo acetyl adenylate is 3.75·10 −4 M, and for pyrophosphate 1.2·10 −3 M. Acetyl deoxy adenylate was found to be a more favourable substrate for the enzyme than acetyl adenylate. The K m value for acetyl dAMP is 4·10 −4 M.

THE ENOLASE OF THE HUMAN ERYTHROCYTE

The enolase activity of the human erythrocyte has been studied with a partially purified preparation of the enzyme. The enzyme was found to have an absolute requirement for Mg2+ions. A kinetic study of the influence of the concentration of Mg ions and 2-phosphoglycerate on the formation of phosphoeno/pyruvate from 2-phosphoglycerate has shown that the active complex of enzyme, substrate, and activator (Mg2+) can be formed in several ways. With low concentrations of substrate and Mg2+the reaction was maximum at pH 7.0; with high concentrations of both, the activity was maximum over a wide range of hydrogen ion concentrations on the acid side of neutrality (at least from pH 6.3 to 7.0) and decreased above pH 7.0.

Sodium-potassium activated G-strophanthin sensitive ATPase in cardiac muscle.

SummaryAn ATPase has been demonstrated in water extracts and microsomal suspensions prepared from rabbit ventricles. It has an absolute requirement for Mg and it can be further stimulated by Na and K. The Na + K active component is susceptible to inhibition by G-Strophanthin. Ageing increases the Mg + Na + K/Mg ATPase ratio.

Partial Characterization of Hexokinase from Euglena gracilis var. bacillaris*

SYNOPSIS. A partially purified hexokinase extracted from Euglena had the following properties: 1) pH optimum 8.0–8.5; 2) an absolute requirement for Mg++ and adenosine triphosphate with Mn++, Co++, Zn++, and Ca++ less active or inactive under the test conditions. Inosine triphosphate could not be substituted for adenosine triphosphate; 3) an apparent Km (glucose) of 5 × 10−4 M; 4) the enzyme was not inhibited by the usual sulfhydryl agents, but was inhibited 24% by adenosine diphosphate. The extract phosphorylated fructose and mannose. It was not clear whether a separate enzyme phosphorylated fructose. Relative rates of phosphorylation, as determined by labile phosphate analyses, were: glucose, 1.00; fructose, 1.19; mannose, 0.56. The partially purified extract also contained phosphohexose isomerase activity; 6‐phosphogluconic acid dehydrogenase was absent. Euglena hexokinase is apparently localized in the cytoplasmic or small‐particle fraction of the cell. In most respects the enzyme seems to resemble the well‐characterized yeast hexokinase rather than the muscle enzyme.

Studies in biosynthesis of polymetaphosphate by an enzyme from Corynebacterium xerosis

1. 1. An enzyme has been partially purified from Corynebacterium xerosis which catalyses the synthesis of polymetaphosphate from ATP. 2. 2. The enzyme was found to be completely inhibited by (NH 4) 2SO 4 and has an absolute requirement for Mg 2+. ADP and AMP inhibited the synthesis at high concentrations. 3. 3. The experimental evidence obtained did not suggest the presence of a phosphate primer. 4. 4. No formation of “acid-soluble” intermediates was detected during the synthesis. 5. 5. Addition of low molecular phosphate polymers made no appreciable difference to the synthesis. 6. 6. The reversibility of the reaction, i.e. synthesis of ATP from ADP and polymetaphosphate, could not be demonstrated with the purified enzyme.

The effect of magnesium on oxidative phosphorylation and mitochondrial adenosine triphosphatase

1. 1. Low concentrations of Mg 2+ stimulate both the ATP-ase activity and oxidative phosphorylation of the mitochondrial sub-unit obtained by treatment of liver mitochondria with digitonin. The stimulation of oxidative phosphorylation is not due to an activation of the hexokinase used to trap the ATP-ase but is due to a requirement for Mg 2+ in oxidative phosphorylation. 2. 2. Concentrations of Mg 2+ above 0.0005 M inhibit the ATP-ase and above 0.001 M inhibit oxidative phosphorylation. The inhibition of oxidative phosphorylation is probably caused by the stimulation by Mg 2+ of the hydrolysis of an intermediate in the oxidative phosphorylation reaction. 3. 3. It is concluded that the Mg 2+-stimulated ATP-ase and the DNP-stimulated ATP-ase differ in the nature of their hydrolytic reaction, but that both contain the same phosphorylation reaction, which is moreover the same as that in oxidative phosphorylation, but in the opposite direction.

Growing Ochromonas malhamensis Above 35°C.*

SUMMARY. Ochromonas malhamensis (Pringsheim strain) can be grown above 35.5°C.; below 35°, the previous chemically defined medium supports dense growth. The B12 and thiamine requirements rise steeply with temperature, and growth promotion by folic acid emerges; folic acid spares the enhanced B12 requirement. B12 is spared also, perhaps wholly bypassed, by purines + pyrimidines + amino acids (below 35°, exogenous purines, pyrimidines, and folic acid have little effect). Requirements also emerge for glycine (spared by serine), valine and isoleucine (their ratio is critical; leucine and threonine assist in maintaining a good balance), and, at very slightly higher temperatures, phenylalanine, tryptophan, cystine, and lysine. Requirements for Mg, Fe, Zn, and Mn appear to rise steeply with temperature; metal toxicities have to be circumvented carefully. The proportion of histidine + arginine to carbohydrate has to be increased, and a Krebs‐cycle component such as succinic acid becomes stimulatory. At 36.3–36.7°, a further supplement of crude natural materials such as an autoclaved suspension of Ochromonas cells is needed. Relevance of these findings to fever stress in vertebrates, general mitochondrial function, and repair of radiation damage, is discussed.

The Requirement for Magnesium Ions in the Inactivation of the Third Component of Human Complement (C′3) by Insoluble Residues of Yeast Cells (Zymosan)

Summary Mg++ is required for the inactivation of C′3 by insoluble residues of yeast cells (zymosan). The concentration of Mg++ in normal serum is more than adequate for the reaction to proceed optimally. The requirement for Mg++ is also demonstrated by the greater uptake of serum nitrogen by zymosan in the presence of Mg++ than in its absence. The inactivation of human C′3 by zymosan appears to be a stoichiometric reaction sharply dependent on temperature, ionic strength and pH. The optimum conditions are at 37 C, ionic strength 0.15 or less, and pH 6.8–8.6. The complex formed upon the addition of zymosan to serum is highly undissociable or results in the destruction of C′3 activity. Attempts to elute C′3 from the zymosan complex were unsuccessful.

Le metabolisme du fructose-1-phosphate dans le foie

1. 1. The mechanism whereby extracts of hepatic tissue convert fructose-1-phosphate to fructose-6-phosphate has been elucidated. 2. 2. F1P is split by aldolase to glyceraldehyde and phosphodioxyacetone. The latter is partly isomerized to glyceraldehyde-phosphate and the two triose-phosphates condense, again under the action of aldolase, to form fructose-diphosphate. In the absence of Mg +2 ions, the reaction does not progress further and only small quantities of F1P disappear, since the equilibrium of the reactions is greatly in favour of this ester. 3. 3. In the presence of Mg +2, fructose-diphosphate is further hydrolyzed by hexose-diphosphatase, giving rise to fructose-6-phosphate and inorganic phosphate. The equilibrium of the aldolase reactions is thereby displaced in favour of F1P disappearance. 4. 4. Complete balances indicate that for each mole of F1P metabolised, 1 mole of glyceraldehyde, 1 2 mole of inorganic P and 1 2 mole of F6P (partly converted to G6P) are formed. Small amounts of F1P and of triose-phosphates disappear by direct hydrolysis. A one-step conversion of F1P into F6P by a phosphofructomutase has been excluded. 5. 5. In the presence of ATP, glyceraldehyde is phosphorylated to glyceraldehyde-phosphate, through the action of a triokinase. The final product, in the incompletely purified preparations used, is F1P, formed through an aldolase-catalyzed condensation of a second molecule of glyceraldehyde with the phosphodioxyacetone formed from glyceraldehyde-phosphate. 6. 6. Various observations have been made on the enzymes involved. The splitting of F1P and FDP appears to be due to a single aldolase, distinctly different from the muscle enzyme. It is equally active on both esters when saturated with substrate but has a hundred times more affinity for the latter than for the former. The hexose-diphosphatase present in the extracts shows an absolute requirement for Mg +2 ions and splits off specifically the phosphate group attached to carbon 1 of FDP. It differs from the enzyme purified by Gomori by a more acid pH optimum. A new enzyme, triokinase has been described and partly purified. In the presence of ATP, it phosphorylates at approximately the same rate D-glyceraldehyde, DL-glyceraldehyde and dioxyacetone.