The reaction of the mutagen 1,1′-hexamethylene-bis[(5-p-chlorophenyl)-biguanide] with guanosine and cysteine

The mutagen 1,1′-hexamethylene-bis[(5-p-chlorophenyl)-biguanide] reacts at 37°C with guanosine and guanine to yield xanthosine or xanthine and oxidizes cysteine to cystine. After treatment of a guanosine-labelled DNA sample from Escherichia coli with the mutagen xanthine could be detected as a reaction product. At a slow rate the mutagen is hydrolysed spontaneously yielding urea, 1,6-hexanediol and 4-chloroaniline. The reaction mechanisms both of the hydrolysis and of the reaction with cysteine and guanosine are discussed.     

Proton nuclear magnetic resonance of minor nucleosides in yeast phenylalanine transfer ribonucleic acid. Conformational changes as a consequence of aminoacylation, removal of the Y base, and codon--anticodon interaction.

The assignments of the resonances of the methyl and methylene groups belonging to the residues dihydro-uridine-16 and -17 (C5 and C6), dimethylguanosine-26, N-2-methylguanosine-10, and 7-methylguanosine-46 of yeast tRNAPhe at low temperature are reported. Observing the high-field proton NMR spectral region at different temperatures, the effects of aminoacylation, removal of the Y base, and codon-anticodon interaction on the tertiary structure of yeast tRNAPhe were investigated. The following are the results of this study. (1) The two dihydrouridine residues of tRNAPhe have different environments in aqueous solution: dihydro-uridine-16 is more shielded than dihydrouridine-17. (2) The ribothymidine residue from the fragment (47--76) of yeast tRNAPhe and from a tRNA with a partially disrupted structure exhibits multiple conformations arising from different stacking modes between the ribothymidine-54 and the guanosine-53 residue. (3) Upon aminoacylation the type of guanosine-53 interaction with ribothymidine-54 in the tRNAPhe changes. (4) Removal of the Y base from the anticodon loop of yeast tRNAPhe weakens the thermal stability of the tertiary interactions. (5) The interaction of two complementary anticodons in the absence of proteins and of ribosomes results in stabilization of the tertiary structure. Codon-anticodon interaction dependent rearrangement of the tertiary structure of yeast tRNAPhe was not observed. The spin-lattice relaxation times of the methyl and methylene groups of the minor nucleosides in yeast tRNAPhe demonstrate that the minor nucleosides undergo rotational reorientation (tau c) in the nano-second range. The observed differences in these tau c values indicate a similarity of structure of tRNAPhe in solution and in crystalline form.     

Shapes of proteins L1, L9, L25, and L30 from the 50S subunit of the Escherichia coli ribosome, determined by hydrodynamic studies.

Proteins L1, L9, L25, and L30, purified by a nondenaturing method from the 50S ribosomal subunit of Escherichia coli A19, have been characterized. The four proteins were studied under conditions which resemble those used for reconstitution experiments. These proteins have S020,W values of 2.0 S, 1.8 S, 1.8 S, and 1.0 S and D20,W values of 8.4 X 10(-7), 9.0 X 10(-7), 14.0 X 10(-7), and 15.0 X 10(-7) cm2/S. Apparent specific volumes at 20 degrees C are 0.738, 0.733, 0.700, and 0.735 mL/g for the four proteins. The respective molecular weights determined by sedimentation equilibrium are 25 000, 17 300, 12 000, and 6500. The intrinsic viscosity values for the four proteins are 4.0, 5.5, 3.6, and 3.2 mL/g. From these hydrodynamic parameters L1 and L9 appear to have globular or at most only slightly elongated shapes, whereas L25 and L30 appear to be definitely globular.     

Reversible inactivation of tRNA nucleotidyltransferase from baker's yeast by tRNAPhe containing iodoacetamide-alkylated 2-thiocytidine in normal and additional positions.

2-Thiocytidine 5'-triphosphate, s2CTP, is able to replace CTP as a substrate for tRNA nucleotidyltransferase. s2CMP can be incorporated into both cytidine sites of the C-C-A terminus common to all tRNAs, and in the absence of ATP into at least two additional positions. This was shown by alkylation of the 2-thiocytidine residues with iodo[14C]acetamide, total nucleoside analysis, microgel electrophoresis and analysis of RNase T1 fragments of these tRNAs. The incorporation of the 3'-terminal AMP is not influenced by the additional s2CMP residues at pH 9.0. However, at pH 7.6 the additional s2CMP residues are hydrolysed and AMP can be incorporated into the normal position. Two different tRNAs with terminal 2-thiocytidine alkylated by iodoacetamide inhibit tRNA nucleotidyltransferase. This inhibition is significantly slower if an elongated species is used compared to a tRNA with alkylated 2-thiocytidine in the normal position 75. The addition of 2-mercaptoethanol reactivates the enzyme and leads to a cytidine containing tRNA. This reaction identifies the attacking nucleophile of the enzyme as cysteine residue, which is probably identical to a cysteine residue found in a similar experiment reported previously. The mechanism of the enzymatic and chemical reactions is discussed.     

Some connections between physiognomic traits and intelligence

A sample of 84 female subjects (students) was taken and split up on the basis of the IST-ratings (“Intelligence Structure Test” by Amthauer) into two extreme groups of “more intelligent” (N = 14) and “less intelligent” (N = 11) subjects with an aim to testing Kozeny's findings. Using his photographic-statistical method, Kozeny had observed that “more intelligent” people have a more open eye, a smaller and straighter mouth, a stronger chin, and—above all in its side dimensions—a better developed forehead. These physiognomic indicators of differences in intelligence were confirmed to a large extent by the measurements taken from the portraits of the subjects.     

Some analytical results about a simple reaction-diffusion system for morphogenesis

Summary The reaction-diffusion system considered involves only one nonlinear term and is a gradient system. In a bifurcation analysis for the equilibrium states, the global existence of infinitely many solution branches can be shown by the method of Ljusternik-Schnirelmann. Their stability is studied. Using a Ljapunov functional it can be shown that the solutions of the time-dependent system converge to the equilibrium states.     

Cyclic 3',5'-adenosine monophosphate in the choroid plexus: stimulation by cholera toxin.

Cholera toxin was found to induce high accumulations of cyclic AMP in the isolated choroid plexus of the rabbit and in the incubation medium. The accumulation showed a characteristic lag phase of at least 30 min and continued for at least 3 hours. Inactivated cholera toxin was unable to increase cyclic AMP levels. There was only a moderate effect of cholera toxin on cyclic AMP “low K_m” phosphodiesterase activity in homogenates. The effect of cholera toxin on cyclic AMP levels confirms the existance of a potent cyclic AMP generating system in the choroid plexus which is activated also by β-adrenergic agonists, histamine and prostaglandin E₁.     

Evaluation of fasciotomy and vasodilator for treatment of frostbite in the dog

Severe freezing injury was produced in the hind foot of 26 mongrel dogs. All dogs were given daily whirlpool treatment and protective bandaging for 14 days following injury. In addition, certain dogs received a vasodilator, fasciotomy, or both vasodilator and fasciotomy following injury. Deep foot temperatures, foot volumes, tissue pressures, and 14 day tissue loss-salvage scores were compared. Significant differences between fasciotomy and nonfasciotomy dogs were seen in foot temperature, volume, and tissue pressure immediately following fasciotomy. Though there was no significant difference in 14 day tissue loss, there was clinically apparent prolongation of integrity of the local vascular system for 2 to 5 days following fasciotomy, and total foot salvage in several dogs receiving fasciotomy.