Preparation of metaphase chromatin of Physarumpolycephalum without the loss of repressed RNA synthesis

A novel method for the preparation of intact chromatin from the slime mold $\text{Physarum}\text{polycephalum>}$ which retains the $\text{in}\text{vivo}$ property of RNA synthesis is described. Preparations from G₂-cells were highly active, while those from metaphase-cells were inactive. The plasmodial cells were disrupted by gentle homogenization on a polyethylene sieve in a neutral isotonic sucrose medium containing Mg⁺⁺, deoxycholate and EGTA, a Ca⁺⁺-chelating agent. The nuclei were lysed in a hypotonic buffer without use of EDTA and chromatin was precipitated by centrifugation after addition of Mg⁺⁺.     

Correlation of mitochondrial cytochrome concentration and activity to oxygen availability in the newborn.

Effect of $\text{in vivo}$ oxygenation on mitochondrial respiratory chain capacity was studied in newborn puppies. Heart mitochondria were isolated from 0 to 7 days. As the arterial PO₂ rises sharply during the first 3–4 days, State 3 respiratory capacity and Ca⁺⁺ transport activity decrease linearly. Cytochrome $\text{c}$ and $\text{a + a}$₃ concentrations increase rapidly. Thus the enzymatic turnover of the respiratory chain decreases to one-fifth of the fetal term value in 4 days. These data are in agreement with earlier results indicating a strong controlling effect of $\text{in vivo}$ oxygenation on mitochondrial respiratory capacity.     

Inhibition by zinc of the binding of C1 to antigen-antibody complexes

Zinc sulphate in the range of 10^?4 to 2×10^?5 M prevents the binding of $\text{C}\text{1}$ to antigen antibody complexes, and the initation of the cascade of events in the classical complement pathway leading to cell lysis. Other heavy metals, Co⁺⁺, Cd⁺⁺, Cu⁺⁺, or Mn⁺⁺ were without effect in this concentration range. Zinc was ineffective when added after $\text{C}\text{1}$ was bound and failed to displace $\text{C}\text{1}$ which was already bound to antigen antibody complexes. The ability of zinc to regulate the binding of the zymogen or activated form of $\text{C}\text{1}$ to antigen-antibody complexes represents a new method of controlling the initiation of the classical complement pathway.     

Biosynthesis of O-acyl ethanediol phosphorylcholine in a cell-free system from rat liver.

1-$\text{0}$-Hexadecanoyl [U-¹⁴C]ethanediol can serve as substrate in the formation of 1-$\text{0}$-hexadecanoyl ethanediol 2-phosphorylcholine by particulate cell-free preparations from rat liver. Catalytic activity is largely associated with the microsomal fraction. The reaction requires CDPcholine and Mg⁺⁺. Phosphatidylcholine cannot substitute for CDPcholine, but Mn⁺⁺ is almost as effective as Mg⁺⁺. Ca⁺⁺ inhibits the reaction. The acyl ethanediol phosphorylcholine produced was identified by repeated cochromotography with authentic diol phospholipid to constant specific radioactivity, and by enzymatic and chemical degradations.     

Influence of Ca++ and Mg++ on the vanadate inhibition of the Ca++- ATPase from pig heart sarcoplasmic reticulum

Vanadate inhibits the Ca⁺⁺-ATPase of sarcoplasmic reticulum from pig heart half maximally at about 10^?5 M. Mg⁺⁺ promotes this inhibition by vanadate whereas increasing Ca⁺⁺-concentrations protect the enzyme against vanadate inhibition. Keeping the ratio $\text{Mg}{}^{\mathrm{++}}\text{ATP}$ constant there was no influence of ATP on the vanadate inhibition at concentrations up to 5 × 10^?3 M ATP. Whenever the ratio $\text{Mg}{}^{\mathrm{++}}\text{ATP}$ was higher than 1:1 the inhibitory effect of vanadate on the Ca⁺⁺-ATPase was increased.     

Basal and potassium stimulated, calcium dependent, endorphins release from pituitary cells.

Mouse pituitary tumor cells grown in tissue culture release endorphins spontaneously to the culture medium. Depolarization of these cells by incubation with high K⁺ concentration (56 mM) increased 2–3 folds the release of endorphins. The K⁺ evoked release was Ca⁺⁺ dependent by that: $\text{a}$, removal of Ca⁺⁺ ions inhibited 90% of K⁺ stimulated release. $\text{b}$, ethyleneglycol-bis (β-aminoethyl ether) N,N′-tetraacetic acid (EGTA) inhibited release of endorphins in the presence of high K⁺ and Ca⁺⁺. It is suggested that dual regulatory system inhibit and/or stimulate $\text{in-vivo}$ release of endorphins from the pituitary glands.     

Guanylate cyclase from Dictyosteliumdiscoideum

Guanylate cyclase from crude homogenates of vegetative $\text{Dictyostelium}$$\text{discoideum}$ has been characterized. It has a pH optimum of 8.0, temperature optimum of 25°C and requires 1 mM dithiothreitol for optimal activity. It strongly prefers Mn⁺⁺ to Mg⁺⁺ as divalent cation, requires Mn⁺⁺ in excess of GTP for detectable activity, and is inhibited by high Mn⁺⁺ concentrations. It has an apparent Km for GTP of approximately 517 μM at 1 mM excess Mn⁺⁺.The specific activity of guanylate cyclase in vegetative homogenates is 50–80 pmoles cGMP formed/min/mg protein. Most of the vegetative activity is found in the supernatant of a 100,000 x g spin (S100). The enzyme is relatively unstable. It loses 40% of its activity after 3 hours storage on ice. Enzyme activity was measured from cells that had been shaken in phosphate buffer for various times. It was found that the specific activity changed little for at least 8 hours. Cyclic AMP at 10^?4 M did not affect the guanylate cyclase activity from crude homogenates of vegetative or 6 hour phosphate-shaken cells.     

Heparan sulphate is a potent inhibitor of DNA synthesis in vitro

The nature and the role of eIF-2 phosphoprotein phosphatase in rabbit reticulocyte lysates have been examined. The eIF-2 phosphoprotein phosphatase is inhibited by a variety of divalent metal ions (Cd⁺⁺>Ag⁺⁺> Cu⁺⁺>Pb⁺⁺>Zn⁺⁺>Co⁺⁺>Sr⁺⁺>Mo⁺⁺) in lysates $\text{in situ}$. In addition, PPi, EDTA and NaF inhibit this enzyme. The eIF-2 phosphoprotein phosphatase is also inhibited by NaHSO₃ and Na₂S₂O₅. Na₂S₂O₅ is, however, more effective. Na₂S₂O₅ has been found to be a potent inhibitor of protein synthesis in lysates. This inhibition is associated with the phosphorylation of the 38,000-dalton subunit of initiation factor eIF-2. eIF-2 overcomes this inhibition. These findings suggest that under optimum conditions of protein synthesis the phosphorylation and dephosphorylation of eIF-2 are in a dynamic state of equilibrium in which dephosphorylation is favored. The inhibition of eIF-2 phosphoprotein phosphatase by Na₂S₂O₅ shifts this equilibrium in favor of eIF-2 phosphorylation, consequently, protein synthesis is inhibited. The sulfhydryl nature of eIF-2 phosphoprotein phosphatase has been established.     

Studies of odd bases in yeast mitochondrial tRNA: III. Characterization of the tRNA methylases associated with the mitochondria

Whereas m¹G, m²G, m₂²G, m⁷G, T, m¹A, m⁵C and Cm methylase activities were found in total cell enzyme of $\text{Saccharomyces cerevisiae}$ using under-methylated $\text{E. coli}$ tRNA and $\text{E. coli}$ B tRNA in reaction with or without Mg⁺⁺, only m¹G, m²G, m₂²G and T methylases occurred in mitochondria. Mitochondrial and cytoplasmic tRNA cannot be methylated by their homologous enzymes; only mitochondrial tRNA can be methylated in a heterologous reaction by total cell enzyme with formation of T, m⁵C, m¹A and low amounts of m²G and m₂²G.     

Shell growth of unfed oysters in the laboratory: A sublethal bioassay system for pollutants

Unfed oysters, $\text{Crassostrea virginica}$ Gmelin, in 12 g/1 commercial grade artificial sea-water supplemented with calcium bicarbonate (approximately 7 mM Ca⁺⁺ and HCO₃^?) deposit shell for four to six weeks. A no-growth critical calcium ion concentration of 1.5 mM was determined in this study. A simple sublethal bioassay system can be developed utilizing the observed shell growth. Significant (p < 0.001) inhibition of shell deposition in oysters subjected to an initial concentration of 0.25 mg Cd⁺⁺/1 demonstrates the efficacy of the proposed method.     

The phosphorylation of troponin B by phosphorylase b kinase in skeletal muscle of mice carrying the phosphorylase b kinase deficiency gene

In skeletal muscle of animals with the phosphorylase $\text{b}$ kinase deficiency gene there is < 1% of the normal activity to convert phosphorylase $\text{b}$ to $\text{a}$ in the presence of Ca⁺⁺, Mg⁺⁺, and ATP (1). Correspondingly, there is < 1% of the normal activity to phosphorylate phosphorylase $\text{b}$. Nevertheless, under the same conditions, these extracts catalyze the phosphorylation of troponin at a rate 57% of normal. Phosphorylase $\text{b}$ converting activity can be sedimented from skeletal muscle of control mice by centrifugation. This fraction isolated from I strain skeletal muscle extracts phosphorylates troponin at a rate 29–39% of the control. EGTA¹ (15 mM) inhibits troponin phosphorylation by 50–60% in this fraction from both strains. The EGTA inhibition is reversed by 15 mM Ca⁺⁺. Thus the phosphorylase $\text{b}$ kinase in skeletal muscle of animals with the phosphorylase $\text{b}$ kinase deficiency gene can phosphorylate troponin B, although it shows little or no activity with phosphorylase as a substrate. This observation is consistent with the normal muscle contractility of I strain animals.     

Coordinated, coenzyme Q reversible, 2,5-dibromothymoquionine inhibition of electron transport and ATPase in Escherichia coli.

2,6-dibromothymoquinone (DBMIB) and other coenzyme Q analogs partially inhibit electron transport and the membrane-bound Mg⁺⁺ stimulated ATPase of $\text{E. coli}$ membranes. The inhibitions by DBMIB are fully reversed by coenzyme Q₆, and other analogs show partial reversal by coenzyme Q₆. Electron transport reactions inhibited are NADH and lactate oxidase, NADH menadione reductase, lactate phenazinemethosulfate reductase and duroquinol oxidase. The concentrations of DBMIB required are similar for electron transport and ATPase inhibition and inhibitions are all increased by uncouplers. Electron transport and ATPase are not inhibited in a DBMIB insensitive mutant. Soluble ATPase extracted from the membranes does not show DBMIB inhibition under either high or low Mg⁺⁺ conditions. Lipophilic chelators show additional inhibition over DBMIB. It appears that coenzyme Q functions at three sites in $\text{E. coli}$ electron transport where ATPase activity is controlled. Coenzyme Q deficient mutants also show decreased electron transport and ATPase activity which is restored by coenzyme Q.     

Acyltransferases and the biosynthesis of pulmonary surfactant lipid in adenoma alveolar type II cells.

Acyltransferases are present in microsomes from alveolar type II cell adenomas (produced by urethan injections) that transfer palmitic acid in the presence of CoA, ATP, and Mg⁺⁺ to $\text{sn}$-glycerol-3-P to form phosphatidic acid, to dihydroxyacetone-P to form acyldihydroxyacetone-P, and to 1-acyl-$\text{sn}$-glycero-3-phosphocholine to form 3-$\text{sn}$-phosphatidylcholine. The data clearly demonstrate that the microsomal preparations can catalyze significant incorporation of palmitic acid into the 2-position of the disaturated species of 3-sn-phosphatidylcholine independently of phosphatidic acid formation as evidenced by the fact that $\text{sn}$-glycerol-3-P and calcium ions (which inhibit choline phosphotransferase) did not influence the incorporation of palmitic acid into the main surfactant lipid. Thus, a deacylation-acylation reaction involving 2-lysophosphatidylcholine appears to be an important pathway for the synthesis of surfactant lipid in alveolar type II cells; the control of acyl specificity at the 2-position is determined by the relative concentrations of the coparticipating substrates, l-palmitoyl-$\text{sn}$-glycero-3-phosphocholine and palmitoyl-CoA.     

Biosynthesis of a P1-2-acetamido-2-deoxy-D-glucosyl P2-polyisoprenyl pyrophosphate by calf pancreas microsomes

Incubation of UDP-[¹⁴C]-$\text{N}$-acetylglucosamine with calf pancreas microsomes in the presence of Mn⁺⁺ and potassium thiocyanate gave a labeled glycolipid, tentatively identified as $\text{P}$¹-2-acetamido-2-deoxy-$\text{D}$-glucosyl $\text{P}$²-dolichyl pyrophosphate on the basis of cochromatography with synthetic $\text{P}$¹-2-acetamido-2-deoxy-α-$\text{D}$-glucopyranosyl $\text{P}$²-dolichyl pyrophosphate, similar chemical and enzymic hydrolyses of the biosynthetic and synthetic compounds, and stimulation of the biosynthesis by addition to the incubation mixture o dolichyl phosphate or a crude lipid fraction extracted from microsomes.     

Rapid alteration in Ca++ content and fluxes in phorbol 12-myristate 13-acetate treated myoblasts

The tumor promoter phorbol 12-myristate 13-acetate rapidly induces alterations in both Ca⁺⁺ content and transport in cultured differentiated chick myoblasts. At 4 ng/ml (6nM), the promoter caused a 25 ± 12% decrease in total intracellular Ca⁺⁺ within 5 h after its addition. Measurement of ⁴⁵Ca⁺⁺ transport at this time revealed a 15 ± 6% decrease in the rate constants for both efflux and influx. Values of $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for the cytosolic Ca⁺⁺ pool in control and treated cells were 9.1 and 10.7 min, respectively, for efflux and 8.6 and 10.4 min, respectively, for influx. Ca⁺⁺ influx was decreased maximally within 90 sec after promoter addition. No effect was observed on ⁸⁶Rb⁺ uptake or intracellular concentration at equilibrium. The Ca⁺⁺ response is among the most rapid yet reported and may play a primary role in altering cellular metabolism.     

Effects of calcium ions and quinolinic acid on rat kidney mitochondrial kynurenine aminotransferase

At pH 6.4, rat kidney mitochondrial kynurenine aminotransferase activity is enhanced several-fold by the addition of CaCl₂, apparently because Ca⁺⁺ facilitates the translocation of α-ketoglutarate, one of the substrates, across the mitochondrial inner membrane. Chloride salts or Mg⁺⁺, Mn⁺⁺, Na⁺, K⁺, and NH₄⁺ did not have this effect. At pH 6.8, the enzyme activity was near maximal even without added Ca⁺⁺ but was strongly depressed by either of two calcium chelating agents, quinolinic acid (Q.A.) and ethyleneglycol-bis(β-aminoethyl ether)N,N′-tetraacetic acid (EGTA). These observations support the view that Ca⁺⁺ is involved in regulating kidney mitochondrial translocation of α-ketoglutarate and that the reported interference of polycarboxylate anion translocation by Q.A. $\text{in vivo}$ depends on the ability of that agent to chelate Ca⁺⁺.     

Effects of thiol modification and Ca++ on agonist-specific state transitions of nicotinic acetylcholine receptor from Torpedo californica electroplax.

The agonist binding affinity of nicotinic acetylcholine receptor (nAChR) from $\text{Torpedo}$$\text{californica}$ electroplax, as inferred from ability of agonist to inhibit specific curaremimetic neurotoxin binding to nAChR, is sensitive to the duration of exposure to agonist. The concentration of carbachol necessary to prevent one-half of toxin binding over a 30 min incubation with nAChR (K₃₀) is 10 μM when toxin and carbachol are simultaneously added to membrane-bound nAChR, and 3 μM when nAChR are pretreated with carbachol for 30 min prior to the addition of toxin. These alterations in agonist affinity may be mimicked by modification of nAChR thiol groups. Affinity of nAChR for carbachol is decreased following treatment with dithiothreitol (DTT). Dithio-bis-nitrobenzoic acid treatment of DTT-reduced membranes yields K₃₀ values of 5 μM for carbachol, while N-ethylmaleimide treatment of DTT-reduced nAChR produces nAChR with reduced affinity for carbachol, reflected in K₃₀ values of about 400 μM. In the absence of Ca⁺⁺, K₃₀ values for carbachol binding to native and DTT-reduced nAChR are diminished 3–6 fold. These affinity alterations are not observed with d-tubocurarine (antagonist) binding to nAChR. Thus, Ca⁺⁺ and the oxidation state of nAChR thiols appear to affect the affinity of nAChR for agonists (but not antagonists), and may therefore be related to agonist-mediated events in receptor activation and/or desensitization.     

The inhibitor effect of probenecid and structural analogues on organic anions and chloride permeabilities in ox erythrocytes

Probenecid inhibits anion movements (organic anions and chloride) in ox erythrocytes. The I₅₀ is 4 · 10^?5 M. Structural analogues such as carinamide, $\text{p-}\text{carboxybenzene}$ sulfonamide and $\text{p-}\text{carboxy}$$\text{N,N}$ diethyl benzene sulfonamide, which are drugs of the sulfonamide class, were also found to inhibit anion transport. These results reinforce the previously discussed view based on structural considerations, that sulfonamides act on the red cell membrane as competitors of anion transport. It is possible that probenecid and carinamide act in a similar way in the kidney.