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At least 19 recordsLinked to original sources
PubMed1978

Interaction of "aza" and "deaza" analogs of adenosine cyclic 3', 5'-phosphate with some enzymes of adenosine cyclic 3', 5'-phosphate metabolism: evidence that the lone pair electrons of N-3 are involved in the binding of adenosine cyclic 3', 5'-phosphate to type II adenosine cyclic 3', 5'-phosphate-dependent protein kinase.

Five hetercyclic analogs of adenosine cyclic 3',5'-phosphate (cyclic AMP) were examined for their ability (1) to stimulate type II cyclic AMP-dependent kinases from bovine brain, bovine heart, and rat liver; (2) to serve as substrates for "high Km" (Km for cyclic AMP = 0.13-0.43 mM) cyclic nucleotide phosphodiesterases from bovine heart, rabbit kidney, and rat liver; and (3) to inhibit the hydrolysis of cyclic AMP catalyzed by "low Km" (Km for cAMP = 0.32-1.5 muM) cyclic nucleotide phosphodiesterases from bovine brain, bovine heart, dog heart, rabbit liver, rat brain and rat liver. The analogs all had a purine ring system which had been modified by replacement of a ring carbon with nitrogen or vice versa to yield 2-aza-cAMP (7-amino-4-beta-D-ribofuranosylimidazo [4,5-d] -v-triazine cyclic 3',5'-phosphate); 8-aza-cAMP (7-amino-3-beta-D-ribofuranosyl-v-triazolo-[4,5-d]-pyrimidine cyclic 3',5'-phosphate); 1 deaza-cAMP (7-amino-3-beta-D-ribofuranosylimidazo [4,5-b[pyridine cyclic 3',5'-phosphate); 3-deaza-cAMP (4-amino-1-beta-D-ribofuranosylimidazo[4,5-c]pyridine cyclic 3',5'-phosphate) and 7-deaza-cAMP (7-amino-4-beta-D-ribofuranosylpyrrolo[2,3-d]pyrimidine cyclic 3',5'-phosphate).

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1976

Studies of phosphate transport in Escherichia coli. I. Reexamination of the effect of osmotic and cold shock on phosphate uptake and some attempts to restore uptake with phosphate binding protein.

1. The first stage of osmotic shock caused a slight reduction in the primary uptake of inorganic orthophosphate (Pi) in AB3311 cells of Escherichia coli which normally exhibit a biphasic type of phosphate uptake. The second stage of osmotic shock resulted in a marked reduction (a total of 80-85%) in the primary uptake phase and a lesser reduction (50%) in the secondary uptake. When osmotically shocked cells are allowed to recover in a phosphate-free, but otherwise complete medium sufficient repair occurs in the shocked cells to overcome growth lags and to restore the above losses in phosphate uptake almost to normal after 90-180 min of recovery. 2. Extensive investigation was made of the more mild cold shock procedure which involves the rapid disperion of Escherichia coli cells into 80 vol. of water at 2 degrees C. The most consistent cold shock effects, as evidenced by reductions in phosphate uptake, were obtained in cells after they were washed in appropriate buffered salts media, suspended in a minimal volume of water and shocked from 37 degrees C rather than 24 degrees C. Less severe shocks were obtained after washing in imidazole/salts/glucose or Tris/salts/glucose media than in NaCl/Tris. 3. A number of attempts were made to restore by the addition of phosphate binding protein the reduction in phosphate uptake of E. coli AB3311 cells caused by a variety of cold shocks. In no instance was good restoration of phosphate uptake achieved. Qualitatively, it appeared that a better restoration of uptake occurred in unstarved and starved cells washed in imidazole/salts/glucose where the cold shock effect was less severe.

Bacterial Proteins↗
PubMed1978

Isotopic (18O) shift in 31P nuclear magnetic resonance applied to a study of enzyme-catalyzed phosphate--phosphate exchange and phosphate (oxygen)--water exchange reactions.

An isotopic shift of the (31)P nuclear magnetic resonance due to (18)O bonded to phosphorus of 0.0206 ppm has been observed in inorganic orthophosphate and adenine nucleotides. Thus, the separation between the resonances of (31)P(18)O(4) and (31)P(16)O(4) at 145.7 MHz is 12 Hz and, in a randomized sample containing approximately 50% (18)O, all five (16)O-(18)O species are resolved and separated from each other by 3 Hz. Not only does this yield the (18)O/(16)O ratio of the phosphate but, more important, the (18)O-labeled phosphate in effect can serve as a double label in following phosphate reactions, for oxygen in all cases and for phosphorus, provided the oxygen does not exchange with solvent water. Thus, it becomes possible to follow labeled phosphorus or labeled oxygen continuously as reactions proceed. Rate studies involving (i) phosphorus and (ii) oxygen are illustrated by continuous monitoring of the exchange reactions between (i) the beta phosphate of ADP and inorganic phosphate catalyzed by polynucleotide phosphorylase and (ii) inorganic orthophosphate and water catalyzed by yeast inorganic pyrophosphatase. In the ADP-P(i) exchange, the P(i) ((18)O(4)) yielded an alpha P((16)O(3) (18)O) and a beta P((18)O(4)), proving that bond cleavage occurs between the alpha P and the alpha-beta bridge oxygen. Among the many additional potential uses of this labeling technique and its spectroscopic observation are: (i) different labeling of each phosphate group of ATP, (ii) to follow rate of transfer of (18)O from a nonphosphate compound such as a carboxylic acid to a phosphate compound, and (iii) to follow the rate of scrambling (for example, of the beta-gamma bridge oxygen of ATP to nonbridge beta P positions) and simultaneously the rate of exchange of the gamma P nonbridge oxygens with solvent water in various ATPase reactions.

Adenosine Diphosphate↗
PubMed1978

The influence of protonation or alkylation of the phosphate group on the e.s.r. spectra and on the rate of phosphate elimination from 2-methoxyethyl phosphate 2-yl radicals.

The e.s.r. spectra of 1-yl, 2-yl and 3'-yl methoxyethyl phosphate radicals derived from CH3OCH2CH2-OPO3H2 by hydrogen abstraction have been measured in aqueous solutions and the hyperfine constants determined. The coupling constants vary strongly with protonation or alkylation of the phosphate group. The 2-yl radicals eliminate phosphate. The rate-constants for the elimination (ke) have been estimated by e.s.r. measurements and by product studies as a function of pH using 60Co gamma-radiolysis. The ke values vary from approximately 0.3 s(-1) for the CH3OCHCH2OPO3--radical and approximately 10(3) s-1 for CH3OCHCH2OPO3H-, to approximately 3 X 10(6) S-1 for CH3OCHCH2OPO3H2. Alkylation of the phosphate group increases the elimination rate-constant to a similar extent as protonation. The results support a recent mechanism which described the OH-radical-induced single-strand breaks of DNA in aqueous solution starting from the C-4' radical of the sugar moiety. It is further concluded the C-4' radical of DNA eliminates the 3'-phosphate group faster than the 5'-phosphate group.

Alkylation↗
PubMed1976

The reactions of D-glyceraldehyde 3-phosphate with thiols and the holoenzyme of D-glyceraldehyde 3-phosphate dehydrogenase and of inorganic phosphate with the acyl-holoenzyme.

D-Glyceraldehyde 3-phosphate forms adducts with thiols. These adducts, which are presumed to be hemithioacetals, equilibrate rapidly with the unhydrated form of the aldehyde, which is the subtrate for D-glyceraldehyde 3-phosphate dehydrogenase. The adduct provides a substrate buffer system whereby a constant low free aldehyde concentration can be maintained during the oxidation of aldehyde by the enzyme and NAD+. With this system, the kinetics of the association of the aldehyde with the enzyme were examined. The rate profile for this reaction is a single exponential process, showing that all four active sites of the enzyme have equivalent and independent reactivity towards the aldehyde, with an apparent second-order rate constant of 5 X 10(7)M-1-S-1 at pH8.0 and 21 degrees C. The second-order rate constant becomes 8 X 10(7)M-1-S-1 when account is taken of the forward and reverse catalytic rate constants of the dehydrogenase. The pH-dependence of the observed rate constant is consistent with a requirement for the unprotonated form of a group of pK 6.1, which is the pK observed for second ionization of glyceraldehyde 3-phosphate. The rate of phosphorolysis of the acyl-enzyme intermediate during the steady-state oxidative phosphorylation of the aldehyde was studied, and is proportional to the total Pi concentration up to at least 1 mM-Pi at pH 7.5. The pH-dependence of the rate of NADH generation under these conditions can be explained by the rate law d[NADA]/dt = k[acy] holoenzyme][PO4(3-)-A1, where thioester bond, although kinetically indistinguishable rate equations for the reaction are possible. The rates of the phosphorolysis reaction and of the aldehyde-association reaction decrease with increasing ionic strength, suggesting that the active site of the enzyme has cationic groups which are involved in the reaction of the enzyme with anionic substrates.

Chemical Phenomena↗
PubMed1978

Effect of phosphate deprivation on renal phosphate transport in the dog.

In order to examine the role of dietary intake of phosphate in regulating renal phosphate transport, clearance and micropuncture studies were performed in 25 dogs with various duration of phosphate deprivation induced by low phosphate diet and aluminum hydroxide gel. In phosphate deprivation of 17-41 days duration, the phosphaturic response to extracellular volume expansion (ECVE) was blunted in the intact group and was virtually abolished in the acutely thyroparathyroidectomized (TPTX) group. With longer phosphate deprivation of 53-110 days, no phosphaturia occurred after ECVE or administration of parathyroid hormone (PTH), even with intact parathyroids. These alterations in phosphaturic responses did not correlate with the plasma phosphate but rather with the duration of phosphate deprivation. Fractional proximal tubule phosphate reabsorption was enhanced in phosphate deprivation and the proximal tubule fluid-to-ultrafilterable phosphate ratio appeared to be a good index for the degree of phosphate deprivation. Acute infusion of phosphate to raise plasma phosphate slightly above normal did not completely restore the responsiveness to ECVE. It is concluded that the adaptive response to phosphate deprivation occurs in both proximal and distal nephron segments and that factors other than plasma phosphate are primarily responsible for such an adaptation.

Animals↗
PubMed1978

The fate of 14C in glucose 6-phosphate synthesized from [1-14C]Ribose 5-phosphate by enzymes of rat liver.

1. Glucose 5-phosphate was synthesized from ribose 5-phosphate by an enzyme extract prepared from an acetone-dried powder of rat liver. Three rates of ribose 5-phosphate utilization were observed during incubation for 17 h. An analysis of intermediates and products formed throughout the incubation revealed that as much as 20% of the substrate carbon could not be accounted for. 2. With [1-14C]ribose 5-phosphate as substrate, the specific radioactivity of [14C]glucose 6-phosphate formed was determined at 1, 2, 5 and 30 min and 3, 8 and 17 h. It increased rapidly to 1.9-fold the initial specific radioactivity of [1-14C]ribose 5-phosphate at 3 h and then decreased to a value approximately equal to that of the substrate at 6 h, and finally at 17 h reached a value 0.8-fold that of the initial substrate [1-14C]ribose 5-phosphate. 3. The specific radioactivity of [14C]ribose 5-phosphate decreased to approx. 50% of its inital value during the first 3 h of the incubation and thereafter remained unchanged. 4. The distribution of 14C in the six carbon atoms of [14C]glucose 6-phosphate formed from [1-14C]ribose 5-phosphate at 1, 2, 5 and 30 min and 3, 8 and 17 h was determined. The early time intervals (1--30 min) were characterized by large amounts of 14C in C-2 and in C-6 and with C-1 and C-3 being unlabelled. In contrast, the later time intervals (3--17 h) were characterized by the appearance of 14C in C-1 and C-3 and decreasing amounts of 14C in C-2 and C-6. 5. It is concluded that neither the currently accepted reaction sequence for the non-oxidative pentose phosphate pathway nor the 'defined' pentose phosphate-cycle mechanism can be reconciled with the labelling patterns observed in glucose 6-phosphate formed during the inital 3 h of the incubation.

Animals↗
PubMed1979

Effect of dietary phosphate intake on phosphate transport by isolated rat renal brush-border vesicles.

Renal brush-border membrane vesicles isolated from rats kept for 6-8 weeks on a low-phosphate diet (0.15% of dry matter) showed a markedly faster Na(+)-dependent phosphate uptake than did membrane vesicles isolated from animals kept on a high-phosphate diet (2% of dry matter). Phosphate-uptake rate by brush-border membrane vesicles isolated from animals on a low-phosphate diet remained significantly increased after acute parathyroidectomy. Dietary adaptation was also observed in animals that had been parathyroidectomized before exposure to the different diets. In animals on the low-phosphate diet parathyrin administration inhibited phosphate uptake by brush-border vesicles only if the animals were repleted with P(i) (5ml of 20mm-NaH(2)PO(4)) 1h before being killed. After acute phosphate loading and parathyrin administration the difference in the transport rate between the two dietary groups remained statistically significant. The results suggest that the adaptation of proximal-tubule phosphate transport to dietary intake of phosphate is reflected in the Na(+)/phosphate co-transport system located in the luminal membrane of the proximal-tubule cell. Since the dietary effects on phosphate transport by brush-border membranes are only partially reversed by acute changes in parathyrin concentration and are also observed in chronically parathyroidectomized animals, the adaptation of the Na(+)/phosphate co-transport system to dietary phosphate intake seems to involve an additional mechanism independent of parathyrin.

Alkaline Phosphatase↗
PubMed1975

Synthesis and antitumor activity of 5'-phosphates and cyclic 3',5'-phosphates derived from biologically active nucleosides.

Syntheses and biological activities of 12 N6-substituted adenosine 5'-phosphates and 15 cyclic 3',5'-phosphates are described. Included among these are the cyclic phosphates of the naturally occurring anticodon adjacent modified nucleosides, N6-(delta2-isopentenyl)adenosine and N-(purin-6-ylcarbamoyl)-L-threonine ribonucleoside. Also reported in this paper are the 5'-phosphates and cyclic phosphates of the cytokinins, N6-benzyladenosine, kinetin ribonucleoside, 3-(chloro-trans-2-buten-2-yl)adenosine,6-o-chlorophenylureidopurine ribonucleoside, and 6-allylureidopurine ribonucleoside. The 5'-nucleotides were prepared by direct phosphorylation of the corresponding ribonucleosides with POCl3 and triethyl phosphate. These compounds were converted to the cyclic 3',5'-phosphates by cyclization of the corresponding 5'-nucleotides with dicyclohexylcarbodiimide. Comparison of the cytotoxicity of the ribonucleosides with their 5'-nucleotides and cyclic 3',5'-nucleotides showed that some of the 5'-phosphates and cyclic phosphates were almost as active as the parent nucleosides. The 5'-nucleotides and the cyclic phosphates were more soluble than the parent nucleosides. The cyclic 3',5'-nucleotides were examined as alternate activators of cAMP-dependent protein kinase from beef heart. While all of the analogs studied showed some activity toward this enzyme, several compounds were more effective than cAMP itself. The analogs were also tested as substrates for cyclic 3',5'-nucleotide phosphodiesterase from beef heart. The N6-alkyl-cAMP analogs were poor substrates for the enzyme, while N6-carbamoyl-cAMP derivatives were inert toward this enzyme. These compounds did not inhibit the phosphodiesterase. Some of the cyclic phosphates exhibited marginal effect in the inhibition of glycogen synthesis in skin slices.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1978

The effects of intravenous phosphate loading on salivary phosphate secretion and plasma parathyroid hormone levels in the sheep.

Adult sheep were given intravenous infusions of a solution of Na2HPO4 and the effects on parotid salivary composition and on plasma parathyroid hormone levels were studied. Infusion of the phosphate solution resulted in increases in the concentration of inorganic phosphate in the plasma and to proportional increases in the concentration and amount of phosphate secreted in the saliva. There was, however, no evidence that the salivary response was dependent upon a change in endogenous parathyroid hormone release. In other studies infusion of bovine parathyroid hormone or stimulation of endogenous hormone release through infusion of EDTA both led to a fall in the concentration of inorganic phosphate in the plasma and to a fall in the concentration and amount of phosphate secreted in the saliva. Taken together these results suggest that the major factor affecting salivary phosphate secretion in these studies was the concentration of inorganic phosphate in the plasma. Parathyroid hormone does not appear to have any direct effect on salivary phosphate secretion in the sheep though it may indirectly influence phosphate secretion through its effects on plasma inorganic phosphate level.

Animals↗
PubMed1977

Phosphate transport in superficial and deep nephrons in phosphate-loaded rats.

We tested the hypothesis that greater phosphate delivery from deep nephrons than from superficial nephrons contributes to the addition of phosphate to the collecting system during phosphate loading. In the first group of eight anesthetized Munich-Wistar rats infused with phosphate and parathyroid hormone (PTH), fractional delivery of phosphate (FDP%) from superficial distal tubules was 56 +/- 6%, significantly less than the amount appearing in the urine, 67 +/- 6% (P less than 0.01). In the second group of six rats, we determined whether this addition of phosphate could be accounted for by a higher FDP% from the deep nephrons. Free-flow micropuncture collections were taken from deep nephrons (ascending limb of the loop of Henle in the papilla), superficial nephrons (distal tubules in the cortex), and urine (duct of Bellini). The FDP% to the ascending limb of the loop of Henle in deep nephrons was 78 +/- 10%, significantly greater than to the distal convoluted tubules in superficial nephrons, 51 +/- 6% (P less than 0.005), and the fractional excretion of phosphate in urine, 72 +/- 10% (P less than 0.05). Although a difference between FDP% in superficial and deep nephrons due to reabsorption in the ascending limb of the loop of Henle cannot be ruled out from the present data, other studies indicate that this interpretation is unlikely. We conclude that greater phosphate delivery by deep nephrons contributes to the addition of phosphate to the collecting system of phosphate-loaded rats.

Animals↗
PubMedDate not supplied

The effect of parathyroid hormone (PTH) and dietary phosphate on the sodium-dependent phosphate transport system located in the rat renal brush border membrane.

The effect of two parameters regulating renal phosphate excretion, namely parathyroid hormone application and dietary phosphate intake, on the transport properties of isolated rat renal brush border membrane vesicles was investigated. In the first set of experiments brush border membrane vesicles from young normal rats injected i.m. with 30 USP parathyroid hormone or i.v. with 1 mg dibutyryl cAMP were compared. PTH and dbcAMP injection decreased specifically the Vmax of the sodium-dependent phosphate transport system by appr. 30%. In a second set of experiments rats were kept on phosphate-rich and phosphate-poor diet and after 6-8 weeks the brush border membranes were isolated. The membranes obtained from phosphate-depleted animals showed a markedly (approximately 100%) higher initial sodium-dependent phosphate uptake than membranes isolated from animals kept on phosphate-rich diet. Again only the sodium-dependent phosphate uptake was affected, sodium-independent phosphate permeability, sodium-dependent D-glucose transport, mannitol permeability and sodium permeability remained unchanged.

Animals↗
PubMedDate not supplied

The use of phosphate in detergents and possible replacements for phosphate.

About 5% of the total phosphate mined worldwide is used in detergents. The chemical form in which phosphate is used in detergents is predominantly pentasodium triphosphate (PSTP). The most significant feature for the use of PSTP in detergents is its ability to form soluble and strong complexes with calcium and magnesium ions. This provides a strong synergism with regard to detergency when PSTP is used in combination with synthetic surfactants. Other important features of PSTP are its ability to disperse dirt in the washing solution, its weak alkalinity, its crystalline form when dry (which enables production of crisp powders) and, last but not least, its toxicological acceptability. The development of PSTP for use in detergents has a history of over 25 years. In certain areas of highly developed countries where effluents from major centres of population can reach stagnant surface waters a rapid increase of eutrophication of these surface waters is observed. Phosphates are being recognized as one of the essential nutrients contributing to the eutrophication and detergents are one of the many sources of phosphate discharged to the environment. This is now causing demands for reduction in or even banning of the use of phosphates in detergents. Major reserach projects and some practical approaches to meeting these demands are described. The potential environmental impact of removing phosphate from detergents remains, however, doubtful, as it has been demonstrated in Sweden that phosphate removal by sewage treatment is the most effective measure to control phosphate discharges. This makes the case of phosphates in detergents an example of how science and technology can become entangled with politics.

Biodegradation, Environmental↗
PubMed1978

Use of glyceraldehyde-3-phosphate dehydrogenase-depleted human erythrocyte ghosts as specific high affinity adsorbents for the purification of glyceraldehyde-3-phosphate dehydrogenase from various tissues.

Human erythrocyte ghosts depleted of glyceraldehyde-3-phosphate dehydrogenase are used as specific high-affinity adsorbents for the purification of glyceraldehyde-3-phosphate dehydrogenase from mouse muscle, liver, kidney and brain. On incubation with the crude tissue homogenates, the depleted ghosts bind glyceraldehyde-3-phosphate dehydrogenase, aldolase, and a few other proteins. Washing the incubated ghosts several times with 5 mM phosphate buffer(pH 8.0) removed several of the non specifically bound proteins. Aldolase can be eliminated from the membrane by incubating the ghosts for 30 min in 5 mM phosphate buffer (pH 8.0)/2mM fructose 1,6-biphosphate, and then washing with the same solution. Glyceraldehyde-3-phosphate dehydrogenase can then be specifically eluted from the ghosts by incubating them with 2 mM NADH in 5mM phosphate buffer (pH 8.0). Although the enzyme from brain appears to bind less strongly to the ghosts it was possible, using this procedure, to purify glyceraldehyde-3-phosphate dehydrogenase from all the tissues investigated. The purified enzyme exhibits high specific activity and migrates as a single band (during SDS polyacrylamide gel electrophoresis) which corresponds to a protomer molecular weight of 37 000.

Animals↗
PubMed1975

Enzymatic synthesis of mannosyl retinyl phosphate from retinyl phosphate and guanosine diphosphate mannose.

A study was conducted to determine whether retinyl phosphate would act as substrate for the enzymatic synthesis of mannosyl retinyl phosphate. Retinyl phosphate, prepared chemically, supported the growth of vitamin A-deficient rats at the same rate as retinol. It also stimulated the uptake of [14C]mannose from GDP-[14C]mannose into total chloroform-methanol extractable lipid. This reaction occurred in the presence of ATP, Mn2+, detergent (Zonyl A), and a membrane-rich enzyme preparation from the livers of vitamin A-deficient rats, provided that a lipid extract of the membrane preparation of alpha-L-lecithin was also added. Total chloroform-methanol-extractable, labeled mannolipid was separated into two principal labeled mannolipids by thin-layer or column chromatography or by differential solvent extraction. The properties of these mannolipids identified them as glycophospholipids: one was identical with authentic synthetic dolichyl mannosyl phosphate, and the other was concluded to be mannosyl retinyl phosphate because of its incorporation of radioactivity from [3H]retinyl phosphate, its rapid hydrolysis by dilute acid, and the formation of substance that cochromatographed with retinol upon its acid hydrolysis. The presence of ATP or GTP was essential for the stimulation of mannolipid synthesis, probably because of their protective action on the substrates against phosphatases present in the crude enzyme fraction. A pH of 6.0-6.2 favored the formation of dolichyl mannosyl phosphate; a higher pH (6.7-7.0) that of mannosyl retinyl phosphate.

Animals↗
PubMed1979

Interaction of phosphate analogues with glyceraldehyde-3-phosphate dehydrogenase.

The glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase catalyzes the oxidative phosphorylation of D-glyceraldehyde 3-phosphate. A variety of phosphonates have been shown to substitute for phosphate in this reaction [Gardner, J. H., & Byers, L. D., (1977) J. Biol. Chem. 252, 5925--5927]. The dependence of the logarithm of the equilibrium constant for the reaction on the pKa2 value of the phosphonate is characterized by a Brłnsted coefficient, betaeq, of approximately 1. This represents the sensitivity of the transfer of the phosphoglyceroyl group between the active-site sulfhydryl residue (in the acyl-enzyme intermediate) and the acyl acceptor on the basicity of the acyl acceptor. Molybdate (MoO42-) can also serve as an acyl acceptor in the glyceraldehyde-3-phosphate dehydrogenase catalyzed reaction. The second-order rate constant for the reaction with molybdate is only approximately 12 times lower than the reaction with phosphate even though the pKa2 of molybdate is 3.1 units lower than the pKa2 of phosphate. The immediate product of the molybdate reaction is the acyl molybdate, 1-molybdo-3-phosphoglycerate. The acyl molybdate, like the acyl arsenate (the immediate product of the reaction when arsenate is the acyl acceptor), is kinetically unstable. At pH 7.3 (25 degrees C), the half-life for hydrolysis of the acyl molybdate, or the acyl arsenate, is less than 2.5 s. Thus, hydrolysis of 1-molybdo- and 1-arseno-3-phosphoglycerate is at least 2000 times faster than hydrolysis of 1,3-diphosphoglycerate under the same conditions. Glyceraldehyde-3-phosphate dehydrogenase has a fairly broad specificity for acyl acceptors. Most tetrahedral oxy anions tested are substrates for the enzyme (except SO4(2-) and SeO4(2-)). Tetrahedral monoanions such as ReO4- and GeO(OH)3- are not substrates but do bind to the enzyme. These results suggest the requirement of at least one anionic site on the acyl acceptor required for binding and another anionic group on the acyl receptor required for nucleophilic attack on the acyl enzyme.

Glyceraldehyde-3-Phosphate Dehydrogenases↗
PubMed1978

[Accumulation of phosphate ions in biological materials, phosphate ion diffusion and electron microscopical investigations of phosphohydrolases (author's transl)].

Isolated unfixed nuclei of mouse liver accumulate different amounts of phosphate ions dependent on pH, temperature and concentration of phosphate ions. At 37 degrees C and pH = 7.2, 8.5 X 10(9) binding places and a stability constant of 2.0 +/- 0,5 . 10(4) l/mol were calculated, the data at 30 degrees C and pH = 6.5 are 4 X 10(9) Nucleus-1 and 6 X 10(3) l/mol. Nuclei fixed by formaldehyde-ethanol or glutaraldehyde do not accumulated phosphate ions. Under conditions of nearly undisturbed diffusion phosphate ions taken up by the nuclei and precipitated by the help of lead ions are detected electron microscopically in the nuclear envelope, preferently in intracisternal space. Nucleoprotein structures do not show enrichments of crystals. These structures are also not stained after precipitation of phosphate ions under conditions of diminuation of diffusion. A possible mode of phosphate binding in cell nuclei and the influence of adsorbed phosphate ions on localization of enzymatic activities are discussed.

Animals↗
PubMed1977

In vitro effects of flavin adenine dinucleotide and dexamethasone phosphate on high molecular weight phosphate compounds in the rat lens.

In order to clarify the pathogenesis of steroid cataracts as one of the side effects from the administration of dexamethasone phosphate (DX), investigations were conducted into the in vitro effects of flavin adenine dinucleotide (FAD) and DX on the macromolecular phosphate compounds separated from the lens supernatant using Sephadex G-50. The author found that phosphate turnover in the macromolecular phosphate compounds was reduced by DX, however, the loss was partially prevented by the addition of FAD. These macromolecular phosphate compounds were identified as nucleic acids, mostly RNA and a small amount of protein. Therefore, the author employed an experiment using the incorporation of tritiated uridine and thymidine into this macromolecular phosphate compounds. The incroporation of uridine-3H into RNA and thymidine-3H into DNA was inhibited by the addition of DX, however, this loss of turnover rate was partially prevented in RNA by the simultaneous administration of FAD, whereas no change was found in the DNA fraction treated with FAD. These results suggest that there is a close relationhip between FAD and the turnover of macromolecular phosphate compounds in the lens and that FAD, as a new physiological role, has an ability to reactivate the depressed turnover of RNA resulting from a DX administration. The possible role of nucleic acid turnover on the pathogenesis of steroid cataracts was discussed with relationship to adrenal dysfunction leading to a phosphorylation insufficiency caused by DX.

Animals↗