Effects of ATP and cyclic AMP on the (Na+ + K+ + 2Cl-)-cotransport system in turkey erythrocytes

As turkey erythrocytes were progressively depleted of ATP by preincubation with dinitrophenol, the (Na+ + K+ + 2Cl-)-cotransport system (assayed by the bumetanide-sensitive fraction of 86Rb+ influx) became less responsive to activation. The dependence upon intracellular ATP concentration was significantly steeper for transport activated by hypertonic shock (halfmaximal activity at 0.7 mM ATP) than for that activated by either epinephrine or cyclic AMP (halfmaximal activity at 1.7 mM ATP). Upon removal of epinephrine or cyclic AMP from cells that had been preincubated with those substances, bumetanide-sensitive transport activity declined sharply, even though the intracellular cyclic AMP concentration was still over 10-fold that required to maximally activate the transport system. These data are in agreement with the notion that the (Na+ + K+ + 2Cl-)-cotransport system in turkey erythrocytes is activated by cyclic AMP, presumably through the 'classical' pathway involving a protein kinase. They do however indicate that some other, as yet undefined aspect of cyclic AMP metabolism is important for the maintenance of transport activity.     

Mechanism of the cerebrovascular effect of piracetam

Piracetam produces a more pronounced effect on cerebral circulation disturbed by hemorrhagic shock as compared with intact animals. Piracetam has a depressant effect on the nervous regulation of cerebral circulation by suppressing the reflex constriction of the vessels in both arterial systems of the brain. The cerebrovascular effects of piracetam are not mediated through the GABAergic bicuculline-sensitive mechanisms, which is supported by experiments where the drug exhibits its effects under the blockade of GABA receptors.     

The conformation properties and conformation stability of streptokinase and its polymer derivative

The properties and conformational stability of the proteinaceous activator of fibrinolysis--native streptokinase--and its derivative obtained by modification with a linear hydrophilic copolymer based on N-vinylpyrrolidone, were studied by the circular dichroism method. It was shown that polymeric modification of streptokinase had no effect on the secondary structure, while the conformational stability of the modified protein to urea was higher than that of the native one. Studies on thermal stability of both native and modified forms of streptokinase showed that the inactivation rate was lower in the modified form as compared to the native one.     

Kinetics of beta-glucuronidase induction by androgen. Genetic variation in the first order rate constant

Measurements of enzyme activity, rates of protein synthesis, and mRNA activity suggest that the induction of beta-glucuronidase in mouse kidney in response to androgen is regulated at a pretranslational level. Following an initial lag period, the rate and extent of induction follow the rules of simple turnover kinetics and can be described in terms of a zero order rate constant for acquisition of mRNA activity (ka) and a first order rate constant for loss of activity (kb). Genetic variation in kb, described here for the first time, alters the half-time and extent of induction. Variation in kb is independent of previously described variation in ka and, unlike changes in ka, is not associated with change in the lag time. The DNA sequences determining kb, like those determining ka, are genetically linked to the structural gene for beta-glucuronidase. Following the removal of androgen, beta-glucuronidase activity, rate of synthesis, and mRNA activity all decline rapidly with half-lives of 1-2 days. Even in the most rapidly inducing strains, this is significantly faster than the half-time for induction determined by kb. Furthermore, genetic variation in kb does not affect the rate of de-induction. These facts suggest that kb may not describe the turnover of beta-glucuronidase mRNA, but rather the turnover of another step in the induction process.     

NMR study of isoleucine transfer RNA from Thermus thermophilus

An NMR and nuclear Overhauser effect (NOE) analysis of Thermus thermophilus tRNAIle1a is presented. This species contains modifications including s2T54 and s4U8 [Horie, N., Hara-Yokoyama, M., Yokoyama, S., Watanabe, K., Kuchino, Y., Nishimura, S., & Miyazawa, T. (1985) Biochemistry 24, 5711-5715]. All the expected secondary and reverse Hoogsteen AU pairs were identified, with one possible exception. The general geometry of the T psi C loop is the same as the Escherichia coli species, and there is NOE evidence for an A9-UA12 triple. Preliminary measurements of solvent exchange rates of internally hydrogen-bonded bases suggest that this tRNA is more stable than previously studied E. coli and yeast tRNAs.     

Manifestations of angina morbidity as a reflection of the self-regulation of the epidemic process in streptococcal infection

The data on the application of the principles of the self regulation of the epidemic process for understanding the annual dynamics of angina morbidity in organized groups of adults are presented. In this case the reservation of group A streptococci occurs in chronic (resident) carriers, whose proportion was found to be 15.8 +/- 2.6%. The epidemic manifestations of morbidity are regulated mainly by the concentration of newly arrived members in the groups, i. e. by the size of the stratum providing the optimum conditions for the parasitization of the streptococcal population. The annual morbidity levels depend essentially not only on the heterogeneity of the group members with respect to their susceptibility to streptococcal infection, but also on the conditions of their accommodation, affecting the transmission of droplet infection. The role of individual risk factors in the variation of the quantitative characteristics of the angina morbidity manifestations under study is calculated.     

Highly polymorphic microsatellite loci in the bank vole (Clethrionomys glareolus)

We describe seven polymorphic, dinucleotide microsatellite loci isolated from bank voles (Clethrionomys glareolus, Rodentia: Muridae) collected from the Wirral Peninsula, United Kingdom. Microsatellites were isolated as part of a long‐term study on the wider effects of host–pathogen interactions of an endemic viral disease. These microsatellites showed between five and 13 alleles per locus in these populations. Observed and expected heterozygosities varied between 0.275 to 0.777 and 0.487 to 0.794, respectively. These markers will allow us to investigate the structure of this bank vole population.     

Antibody-targeted photolysis: in vitro immunological, photophysical, and cytotoxic properties of monoclonal antibody-dextran-Sn(IV) chlorin e6 immunoconjugates.

A set of anti-melanoma immunoconjugates were prepared which contained chlorin e6: antibody molar ratios of 18.9:1, 11.2:1, 6.8:1, and 1.7:1. All immunoconjugates retained antigen binding activity regardless of the chromophore:antibody substitution ratio that was attained. In contrast, the ground-state absorption spectra of the immunoconjugates showed features which appeared to be dependent on the chromophore:antibody molar ratio. In addition, the quantum yield of singlet oxygen generated by the conjugated chromophores was observed to be significantly less than that observed with the unbound dye. Time-resolved absorbance spectroscopy of the chromophore excited triplet state indicated that the loss of singlet oxygen quantum yield resulted from diminished chromophore triplet yield. Analysis of data obtained from in vitro photolysis of target melanoma cells, in combination with that obtained from the immunochemical and photochemical studies, indicates that the observed immunoconjugate phototoxicity can be reasonably quantitatively represented by (1) the ability of the immunoconjugate to bind SK-MEL-2 cell surface antigen, (2) the amount of chromophore localized at the target cells by immunoconjugate binding, (3) the delivered dose of light at 634 nm, and (4) the singlet oxygen quantum yield of the antibody-bound photosensitizer. Though these data argue strongly for photolysis by the cumulative dosage of singlet oxygen at the cell membrane, nonetheless, the concurrent photoinduced release of other cytotoxic agents should not be ruled out.     

Sex difference in maximal oxygen uptake. Effect of equating haemoglobin concentration

Ten men and 11 women were studied to determine the effect of experimentally equating haemoglobin concentration ([Hb]) on the sex difference in maximal oxygen uptake (VO2max). VO2max was measured on a cycle ergometer using a continuous, load-incremented protocol. The men were studied under two conditions: 1) with normal [Hb] (153 g X L-1) and 2) two days following withdrawal of blood, which reduced their mean [Hb] to exactly equal the mean of the women (134 g X L-1). Prior to blood withdrawal, VO2max expressed in L X min-1 and relative to body weight and ride time on the cycle ergometer test were greater (p less than .01) in men by 1.11 L X min-1 (47%), 4.8 ml X kg-1 min-1 (11.5%) and 5.9 min (67%), respectively, whereas VO2max expressed relative to fat-free weight (FFW) was not significantly different. Equalizing [Hb] reduced (p less than .01) the mean VO2max of the men by 0.26 L X min-1 (7.5%), 3.2 ml X kg-1 min-1 (6.9%) or 4.1 ml X kg FFW-1 min-1 (7.7%), and ride time by 0.7 min (4.8%). Equalizing [Hb] reduced the sex difference for VO2max less than predicted from proportional changes in the oxygen content of the arterial blood and arteriovenous oxygen content difference during maximal exercise. It was concluded that the sex difference in [Hb] accounts for a significant, but relatively small portion of the sex difference in VO2max (L X min-1). Other factors such as the dimensions of the oxygen transport system and musculature are of greater importance.     

Chromosomal location and cloning of the gene (trmD) responsible for the synthesis of tRNA (m1G) methyltransferase in Escherichia coli K-12

Summary The trmD gene, which governs the formation of 1-methyl-guanosine (m¹G) in transfer ribonucleic acid (tRNA), has been located by phage P1 transduction at 56 min on the chromosomal map of Escherichia coli. Cotransduction to tyrA at 56 min is 80%. From the Clarke and Carbon collection a ColE1-tyrA ⁺ hybrid plasmid was isolated, which carried the trmD ⁺ gene and was shown to over-produce the tRNA (m¹G)methyltransferase. By subcloning restriction enzyme fragments in vitro, the trmD ⁺ gene was located to a 3.4 kb DNA fragment 6.5 kb clockwise from the tyrA ⁺ gene. The mutation trmD1, which renders the tRNA (m¹G) methyltransferase temperaturesensitive both in vivo and in vitro could be complemented by trmD ⁺ plasmids. These results suggest that the gene trmD ⁺ is the structural gene for the tRNA (m¹G)methyltransferase (EC 2.1.1.3.1).