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PubMed1979

Identification, characterization and localization of a (Ca2+ + Mg2+)-activated purine nucleoside triphosphate phosphohydrolase from calcifying cartilage.

A purine nucleoside triphosphate phosphohydrolase (unspecified diphosphate phosphohydrolase, EC 3.6.1.15) was chromatographically separated from the bulk of alkaline phosphatase activity by gel filtration chromatography of butanol and EDTA extracts of fracture callus and bovine epiphyseal cartilage. The callus enzyme differed from alkaline phosphatase in a variety of characteristics. The purine nucleoside triphosphate phosphatase hydrolyzed a more specific group of substrates, required Ca2+ and Mg2+ for optimal activity, remained unaffected by a potent alkaline phosphatase inhibitor, and demonstrated a narrower range of optimal pH for catalytic activity. The enzyme was localized in the microsomal pellet following subcellular fractionation of callus chondrocytes. These characteristics indicate a role for the enzyme in Ca2+ transport.

Alkaline Phosphatase↗
PubMed1978

Cytochemical localization of adenylate cyclase and of calcium ion, magnesium ion-activated ATPases in the dense tubular system of human blood platelets.

Cytochemical techniques have been employed to study the localization of adenylate cyclase and (Ca2+ + Mg2+)-stimulated ATPase activities in platelets after fixation. Biochemical analysis of adenylate cyclase demonstrated a 70% reduction in activity in homogenates from fixed cells, but the residual activity could be stimulated 10--20 times by prostaglandin E1 (1 micrometer) under the same incubation conditions as employed in the cytochemical studies (e.g. media containing 2 mM lead nitrate and 10 mM NaF). Adenylate cyclase activity employing 5'-adenylyl-imiodiphosphate (AMP-P(NH)P) as substrate was found to be associated with the dense tubular system (smooth endoplasmic reticulum) in intact fixed platelets, and was apparent only when the cells were incubated with prostaglandin E1. Less activity was found along the membranes of the surface connected open canalicular system and occasionally at the outer cell surface. Enzymatic activity was blocked by the adenylate cyclase inhibitor 9-(tetrahydro-2-furyl) adenine and was not due to AMP-P(NH)P phosphohydrolase activity. The low adenylate cyclase activity in the surface membranes may be due to enzyme inactivation as a result of fixation, since a surface membrane fraction obtained by the glycerol lysis technique from unfixed cells had an adenylate cyclase specific activity equivalent to that in the microsomal membrane fraction. (Ca2+ + Mg2+)-stimulated ATPase activity was found associated with the membranes of the surface connected open canalicular system in unfixed cells. After brief fixation (5--15 min) with glutaradehyde, strong (Ca2+ + Mg2+)ATPase activity became apparent in the dense tubular system. Longer periods of fixation inactivated enzymatic activity. Addition of Ca2+ (1.0 mM) to incubation medium with low Mg2+ (0.2 mM), or increasing Mg2+ to 4.0 mM, in both cases strongly stimulated enzyme activity. The ATPase activity in the platelet membranes was not inhibited by ouabain. It is suggested that the Ca2+-stimulated ATPase and adenylate cyclase activities in the dense tubules may possibly be involved in regulation of intracellular Ca2+ transport.

Adenylyl Cyclases↗
PubMed1979

Functional interactions of lipids and proteins in rat intestinal microvillus membranes.

Interactions of lipids and proteins in isolated rat intestinal microvillus membranes were examined by studying the temperature dependence of enzyme activities and of D-glucose transport in relation to the membrane lipid thermotropic transition observed by fluorescence polarization (26 +/- 2 degrees C) and differential scanning calorimetry (23--39 degrees C). Two groups of activities were defined. Enzymes of the first group, comprising lactase, maltase, sucrase, leucine aminopeptidase, and gamma-glutamyl transpeptidase, all yielded a single slope on the Arrhenius plot in the range 10--40 degrees C and did not appear to experience functionally the effects of the lipid thermotropic transition. Each activity of the second group, comprising calcium- and magnesium-dependent adenosine triphosphatases, p-nitrophenylphosphatase, and D-glucose transport, showed a change in the slope of the Arrhenius plot in the range 25--30 degrees C, corresponding to the lower region of the lipid transition. The terms "extrinsic" and "intrinsic" activities could be applied to these groups. Delipidation of the particulate p-nitrophenylphosphatase removed the discontinuity in the Arrhenius plot. Subsequent relipidation with a variety of lipids restored a break point, but the temperature corresponded to the original discontinuity (25--29 degrees C) rather than to the phase transition temperature of the exogenous lipid added.

4-Nitrophenylphosphatase↗
PubMed1979

Occurrence and role of tightly bound adenine nucleotides in sarcoplasmic reticulum of rabbit skeletal muscle.

Freshly isolated sarcoplasmic reticulum vesicles contain 0.05 mol of tightly bound ADP and 0.03 mol of tightly bound ATP per mol of Ca2+, Mg2+-ATPase (ATP phosphohydrolase, EC 3.6.1.3). These values were increased to 0.1-0.2 mol ADP and 0.2-0.3 mol ATP per mol of ATPase after incubation of vesicles in the presence of MgATP and Ca2+ at 25 degrees C and pH 7.0. Half-maximal enrichment of tightly bound nucleotides was obtained with 2.5 mM ATP and 0.32 microM free Ca2+. Uncoupling of calcium transport from ATPase activity by mild acidic conditions or with ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid at pH 7.0 decreased the ability of the membranes to be enriched with tightly bound nucleotides and also decreased the content of tightly bound nucleotides of previously enriched membranes. Tightly bound [3H]nucleotides could only be partially displaced by reincubation under enrichment conditions. Tightly bound nucleotides are associated with energized calcium translocation but do not appear to be directly involved in the catalytic cycle.

Adenine Nucleotides↗
PubMed1978

Transport of nicotinamide adenine dinucleotide in an unc mutant of Escherichia coli.

The presence and some properties of an NAD+ transport system were examined in PA5, a Mg, Ca-ATPase [EC 3.6.1.3]-defective mutant strain of Escherichia coli W2252. NAD+ uptake was stimulated by exogenous energy sources and dependent on external substrate concentrations with an apparent Km of about 25 micrometer. Most of the radioactivity from [14C]-NAD+ accumulated in the cells was identified as NAD+. [14C]NAD+ uptake was competively inhibited by unlabeled NAD+, NADP+, NMN+ or nicotinamide. Similar uptake activity was also observed in W2252.

Biological Transport↗
PubMed1978

Action of caffeine on calcium transport by isolated fractions of myofibrils, mitochondria, and sarcoplasmic reticulum from rabbit heart.

We studied the effects of caffeine on calcium transport by subcellular organelles isolated from rabbit myocardium. Caffeine increased myofibrillar basic and calcium-activated ATPase activity at 20 mM but not at lower concentrations. Mitochondrial and sarcoplasmic reticulum (SR) calcium accumulation was measured both by dual wavelength spectrophotometry with the calcium-sensitive dye, murexide, and by Millipore filtration with 45Ca. In mitochondria, caffeine impaired phosphate-assisted calcium transport but did not alter the closely related parameters of oxygen uptake, P/O ratio (nmol adenosine diphosphate consumed/n ats oxygen consumed, state 3 respiration) or limited calcium loading. In SR, caffeine impaired calcium accumulation. New methods were used to characterize calcium accumulation in the absence of oxalate according to first order reaction kinetics. Caffeine increased the rate constant while decreasing the calcium accumulated. It also increased the associated calcium-activated ATPase activity at low (30 mM) but not high (240 micrometer) external calcium concentration. In the presence of oxalate, caffeine decreased the rate of calcium accumulation, more with low than high calcium concentration. Net efflux of 45Ca from preloaded SR also was increased by caffeine. The findings indicate that caffeine impairs active calcium accumulation by making SR vesicle membranes more permeable to calcium.

Animals↗
PubMed2025

Blood Pressure Genetics in Han Taiwanese With Cross-Trait Analysis in East Asians: Insights Into Comorbidities, All-Cause Mortality, and Cardiovascular Mortality.

BACKGROUND: Hypertension is a major health burden in East Asia. However, the genetic architecture and clinical implications of blood pressure (BP) traits remain underexplored beyond European-focused studies. This large-scale study aimed to investigate hypertension, systolic BP, and diastolic BP, to uncover genetic links to comorbidities and mortality in Han Taiwanese individuals. METHODS: This large-scale study used China Medical University Hospital biobank data and conducted genome-wide association studies on 25 523 hypertension cases and 47 522 controls, plus 66 236 individuals for systolic BP and 66 152 for diastolic BP. Cross-trait genetic correlations were assessed across 5 East Asian biobanks. Mendelian randomization and polygenic risk scores were applied to assess causality and predict clinical outcomes. RESULTS: We identified 8 loci and 36 genes for hypertension, 7 loci and 17 genes for systolic BP, and 9 loci and 26 genes for diastolic BP. ATP2B1 and FGF5 were common to all BP traits, implicating calcium signaling and vascular remodeling pathways. Cross-trait analyses showed shared genetic liability between BP traits and cardiovascular and metabolic comorbidities. Phenome-wide association studies confirmed strong associations with circulatory diseases. Mendelian randomization analyses demonstrated that elevated BP causally increases the risk of unstable angina pectoris. Polygenic risk scores predicted significantly higher risks and earlier onset of unstable angina pectoris, all-cause mortality, and cardiovascular mortality among individuals in the top polygenic risk score quintiles. CONCLUSIONS: Our findings highlight the genetic basis of BP and comorbidities in East Asians, suggesting that BP genetic risk may inform future approaches to early risk assessment and prevention.

Aged↗
PubMed1978

The role of creatine phosphokinase in supplying energy for the calcium pump system of heart sarcoplasmic reticulum.

An investigation of isolated and purified heart sarcoplasmic reticulum performed in the current study indicates the presence of significant creatine phosphokinase (CPK) activity in this preparation. The localization of CPK on the membrane of sarcoplasmic reticulum has been revealed also by an electron microscopic histochemical method. Under the conditions of the Ca(2+)-ATPase reaction in the presence of creatine phosphate, the release of creatine into the reaction medium is observed, the rate of the latter process being dependent on the MgATP concentration in accordance with the kinetic parameters of the Ca2+-ATPase reaction. CPK localized on the reticular membrane is able to maintain the high rate of calcium consumption by the sarcoplasmic reticulum vesicles. The results obtained demonstrate the close functional coupling between CPK and Ca2+-ATPase in the membrane of sarcoplasmic reticulum and indicate the important functional role of CPK in supplying energy for the Ca(2+)-ATPase reaction and ion transport across the membrane of heart sarcoplasmic reticulum.

Animals↗
PubMed1979

[Biochemical mechanisms for the effect of alcohol on the brain].

This paper reviews and discusses basic knowledge of biochemical mechanisms of action of ethanol upon the central nervous system, the emphasis being on effects upon cerebral membrane structures and processes as well as mechanisms of chemical synaptic transmission. Results of detailed studies into material and steric changes in membranes, ion-dependent adenosine triphosphatases, variations in ion balance, effects upon cyclic nucleotides, influences on special transmitter systems, and mechanisms of formation of morphine-analogous condensation products are presented. In addition, open questions are derived and formulated in problem complexes.

Acetaldehyde↗
PubMed1979

[Studies of the presence of enzymes in various tissues of swine. 5. Studies of the activity and properties of adenosine triphosphatases in the pancreas].

Studies were conducted into the activities of magnesium-ATPase, sodium-potassium-ATPase, and HCO3-ATPase in homogenates of pancreas of 19 foetuses, with body weights between 340 g and 1,642 g, two piglets, with body weights of 9 kg and 10 kg, and four adult pigs. While general enzyme activity was low during foetal development, highest activies usually were recordable from HCO3-ATPase. High activities were recorded from both the piglets and adult pigs. The highest data, again, were recordable from HCO3-ATPase which is essential to the secretion of HCO3 ions. Maximum activity of magnesium-ATPase was based on an ATP-magnesium ratio of 1:1. HCO3-ATPase was best activated by 25 mM NaHCO3 and exhibited high stability to temperature. The activities of magnesium-ATPase and of HCO3-ATPase were inhibited by 10 mM of Rhodanid. Calcium-ATPase reached its maximum activity in response to 5 mM calcium concentration.

Adenosine Triphosphatases↗
PubMed1979

[Role of calcium in realization of nervous control during RNA synthesis in skeletal muscles].

The effects of Ca2+ on the RNA polymerase activity of the nuclei isolated from normal and denervated gastrocnemius muscles of the rabbit were studied. It was shown that 18 hrs after denervation the RNA synthesis in vitro, Ca2+ content and the Ca, Mg-ATPase activity of the nuclei are decreased. After addition of exogenous Ca2+ the incorporation of labelled UTP into the nuclei is stimulated in the denervated muscle and is inhibited in the control. Electrostimulation of the denervated muscle at the peripheral part of the sciatic nerve for 3 hrs increases both the RNA synthesis in the nuclei and the Ca2+ content, as well as the Ca, Mg-ATPase activity. Exogenous Ca2+ has an inhibitory effect on the nuclei of the stimulated muscle. The correlation established is indicative of participation of Ca2+ in the transmission of excitation in skeletal muscle sarcolemma to the processes occurring in nuclear structures.

Animals↗