Primary structure of the alpha-subunit of Torpedo californica (Na+ + K+)ATPase deduced from cDNA sequence

Sodium- and potassium-dependent ATPase [(Na+ + K+)ATPase], which is responsible for the active transport of Na+ and K+, is distributed universally among animal cell membranes and consists of two types of subunits, alpha and beta (refs 1-4). The larger alpha-subunit with a relative molecular mass (Mr) of 84,000-120,000 is thought to have the catalytic role. We have now cloned and sequenced DNA complementary to the Torpedo californica electroplax messenger RNA encoding the alpha-subunit of (Na+ + K+)ATPase and have deduced the complete amino-acid sequence of the polypeptide. Some structural features of the alpha-subunit molecule related to the function of this active-transport protein are discussed.

Depolarizing neuromuscular blocking action induced by electropharmacological coupling in the combined effect of paeoniflorin and glycyrrhizin

Twitch tensions of indirectly stimulated diaphragm muscles of mice were blocked by a combination of paeoniflorin (PF) and glycyrrhizin (GLR). The mechanism of this effect was studied electropharmacologically. When twitch responses were completely prevented, miniature end-plate, end-plate, and muscle action potentials were still observed when PF and GLR were combined, suggesting that the mechanism is postsynaptic. Potential amplitudes induced by acetylcholine (ACh), which was injected iontophoretically, were inhibited by about 70% by PF (25 micrograms/ml) plus GLR (75 micrograms/ml), although neither agent alone caused an inhibition. The combined ratio (PF:GLR = 1:3) by concentrations (g/ml) potentiated both the inhibition of ACh potential amplitudes and the depolarization of resting membrane potentials. These results indicate that the effect of combined PF and GLR is to depolarize the muscle membrane and to block ACh-receptor-linked processes. In chemically skinned (saponin-treated) muscles, the tension induced by 0.39 microM of free calcium was inhibited by PF (300 micrograms/ml), but it tended to be increased by GLR (300 micrograms/ml). Caffeine-induced contractures in the skinned muscles was not influenced by PF, and they tended to be decreased with GLR treatment. Thus, in muscles with sustained depolarization, these combined compounds seem to block intracellular Ca2+ movement.

Blocking effects of a new component, paeoniflorigenone, in paeony root on neuromuscular junctions of frogs and mice

A new monoterpene, paeoniflorigenone (PFG) (100-900 micrograms/ml), which was isolated from paeony roots and identified chemically, suppressed both indirectly and directly stimulated muscle twitchings of frog sciatic nerve-sartorius muscle preparation, and it indirectly stimulated muscle twitchings of phrenic nerve-diaphragm muscle preparations. The suppression effect by PFG (300 micrograms/ml) on twitching was not reversed by neostigmine (60 micrograms/ml) and was restored by washing out of PFG. PFG (150 micrograms/ml) depolarized the diaphragm muscle membranes by 10 mV and did not change the electrotonic potentials. PFG (100 micrograms/ml) inhibited weakly acetylcholine (5 micrograms/ml)-induced slow contractions. These results demonstrated that PFG is a depolarizing neuromuscular blocking agent, being similar to succinylcholine, except that PFG did not produce any contraction, but succinylcholine did.

High guanine plus cytosine content in the third letter of codons of an extreme thermophile. DNA sequence of the isopropylmalate dehydrogenase of Thermus thermophilus

In studies on the cause of the extreme stability of the macromolecules of Thermus thermophilus HB8, the leuB gene coding for 3-isopropylmalate dehydrogenase of the leucine synthesis pathway and its flanking regions were cloned and sequenced. The leuB gene of T. thermophilus was expressed in a leuB-less mutant of Escherichia coli, and thermostable dehydrogenase was purified from an extract of the cells. The primary structure of the thermophilic isopropylmalate dehydrogenase was deduced from the nucleotide sequence leuB gene (1017 base pairs) and the amino acid sequence of the peptides isolated from the purified dehydrogenase. The thermophilic dehydrogenase has Mr = 35,968, and the value was close to that determined for the monomer of dehydrogenase (36,000) by gel electrophoresis. The molecular weight of active dimeric dehydrogenase was found to be 73,000 by high speed liquid chromatography. The primary structure of dehydrogenase was consistent with the amino acid composition of the dehydrogenase. In contrast to the isopropylmalate dehydrogenase of E. coli which contains 8 cysteine residues, there was no cysteine in thermophilic isopropylmalate dehydrogenase. The 5'-noncoding region contained a typical Shine-Dalgarno sequence. The guanine plus cytosine content of the coding region was 70.1%, and that of the third letter of the codons was extremely high (89.4%).

Genes and pseudogenes for mouse U1 and U2 small nuclear RNAs

Regions of the mouse genome homologous to U1 and U2 small nuclear RNAs have been isolated. The U1 regions are identified as pseudogenes on the basis of: 1) insertions, deletions, and substitutions in the sequence of the DNA as compared with that of U1 RNA; 2) absence of complementary RNA in mouse tissues; and 3) lack of expression upon microinjection in Xenopus oocyte nuclei. A U2 region is identified as a gene on the basis of near identity of sequence with U2 RNA and capacity to direct the synthesis of U2-like RNA in Xenopus oocyte nuclei. Both U1 and U2 sequences are repeated in the mouse genome, the U2 sequences analyzed here in an inverted repeat arrangement.

Close structural resemblance among small nuclear RNAs

The published primary and secondary structures of small nuclear RNAs (snRNAs) (1-9) were reexamined and a new common model for their secondary structures was proposed. What is surprising is the resemblance of their secondary structures. U1, U2, U4, and U5 snRNAs share a common sequence of A(U)nG (n greater than or equal to 3) at the single-stranded junction between two hairpins. U6 RNA does not have the A(U)nG sequence, however, all of its possible loops have common sequences with those of U1 RNA at exactly the same positions. Other remarkable common sequences are also noted and their possible biological significance is discussed.

The emergence of Schistosoma japonicum cercariae from Oncomelania quadrasi

The release of Schistosoma japonicum cercariae from Leytean Oncomelania quadrasi snails was observed under laboratory conditions. Two patterns of emergence were noted. The initial, nonperiodic emergence occurred immediately after submerging the snails in water and was followed by a periodic, diurnal emergence which peaked in the afternoon. The daily cercarial output of the periodic emergence appeared to be affected by exogenous light intensity. Furthermore, there was a cessation or reduction in cercarial output every 3rd or 4th day.

Serial implantations of larval Schistosoma mansoni from infected to uninfected snails

The long-term maintenance of Schistosoma mansoni in intermediate snail hosts is described. Snails were infected with one or five miracidia to obtain the initial parasitized liver tissue. The serial implantations were conducted. When the materials for serial implantation were obtained 20 to 60 days after the hosts had begun to release cercariae, the proportion of snails becoming infected was higher than when materials obtained earlier were used. It made no difference whether the initial infection was with one or five miracidia. Our findings suggest the possibility of cloning of unisexual infections in experimental infections.

Kietics of thermal unfolding and refolding of thermostable phosphoglycerate kinase

The kinetics of denaturation by guanidine hydrochloride (GuHCl) of a thermostable phosphoglycerate kinase (PGK) extracted from Thermus thermophilus and of yeast PGK at neutral pH were studied by circular dichroism. Denaturation by GuHCl proceeded as a first-order reaction. The activation free energy of the denaturation reactions (delta Gf not identical to ) in the absence of GuHCl was estimated to be 32.7 kcal/mol for T. thermophilus PGK and 27.9 kcal/mol for yeast PGK (at 25 degrees C). Measurements of the rate constants at various temperatures indicated that delta Gf not identical to has maximum values at 29 degrees C for T. thermophilus PGK and at 20 degrees C for yeast PGK, and that the temperature dependences of delta Gf not identical to, delta Hf not identical to, and delta Sf not identical to for T. thermophilus PGK are smaller than those of yeast PGK. Values of delta Sf not identical to for thermal denaturation for both PGK's are approximately 200 e.u.

Purification and properties of phosphoglycerate kinase from Thermus thermophilus strain HB8

(1) A glycolytic enzyme, phosphoglycerate kinase [EC 2.7.2.3], was purified from cells of an extreme thermophile, Thermus thermophilus strain HB8. The enzyme was resistant to heat, and no loss of activity was observed after incubation for 10--20 min at 79 degrees C. (2) Catalytic properties such as pH optimum (pH 6--8.5), kinetic parameters (Km=0.28 mM for ATP, 1.79 mM for glycerate 3-phosphate), substrate specificity and inhibitors of the enzyme were investigated and compared with those of phosphoglycerate kinase from other sources. (3) The enzyme protein consists of a single polypeptide chain of molecular weight 44,600. The isoelectric point is 5.0 The amino acid composition of the enzyme was studied. The contents of ordered secondary structures were estimated to be 29% alpha-helix and 11% pleated sheet from the circular dichroic spectrum of the enzyme protein. (4) The fluorescence spectrum of the enzyme protein showed an emission maximum at 320 nm when excited at 280 nm. The quantum yield was 0.19. Tryptophyl fluorescence was not quenched, in contrast to the fluorescence reported for yeast phosphoglycerate kinase.

Anomalous fluorescence of yeast 3-phosphoglucerate kinase

The 3-phosphoglycerate kinase (EC 2.7.2.3) of yeast which contains two tryptophyl and eight tyrosyl residues per molecule, displayed an unusualy fluorescence emission spectrum with a maximum at 308 nm when excited at 280 nm. The emission peak shifted to 329 nm when excited at 295 nm. We could confirm that it was due to the efficient quenching of tryptophyl fluorescence as well as to the incomplete energy transfer from tyrosyl to tryptophyl residues. The average fluorescence quantum yield of this protein was 0.076 (excitation at 280 nm) and that of tryptophyl residues was 0.046 (excitation at 295 nm). As the pH of the solution was lowered, the fluorescence intensity of phosphoglycerate kinase at 329 nm dramatically increased between pH 5 and 4, while the position of the peak remained unchanged. When denatured in 4 M guanidine hydrochloride, the protein showed two emission peaks, one at 343 nm and the other at 303 nm.