Isolation of lysine codon suppressors inEscherichia coli

Starting with anEscherichia coli strain containingglyT56, a glycine transfer RNA suppressor of the arginine codons AGA and AGG, and atrpA mutant containing lysine at position 211 of the tryptophan synthetase alpha chain, we have isolated AAG-suppressors that fall into two classes. In class 1 are dominant suppressors that arose with the simultaneous loss ofglyT56 activity. They are approximately 50% cotransducible withargE, as isglyT, and appear to be derived fromglyT56. Class 2 suppressors, located betweenpurE andtrp on theE. coli map, are not near any glycine tRNA genes, and may represent novel missense suppressors.     

Sub-antarctic House mice: colonization, survival and selection

House mice have colonized and survived successfully on a number of Sub-Antarctic islands, where the mean annual temperature is only about 5°C, but where there is little seasonal fluctuation in climate. Surprisingly this allows almost continuous breeding. On at least two islands (Macquarie and Marion), there are significant changes in gene frequency in electro-phoretically detected enzymes between young (less than three months of age) and old animals from the same population. This indicates natural selection acting in opposite directions at different stages of the life cycle. However the genetical compositions of the Macquarie and Marion populations are more distinct from each other than either is from most British samples. This means that detailed studies of the Sub-Antarctic mouse populations are likely to reveal much about local adaptation, while comparison between the responses of different populations may lead to important generalisations about the possible reaction to evolutionary challenges of a species living close to its physiological limit.     

Termination of early pregnancy by ONO-802 suppositories (16,16-dimethyl-trans-Δ-PGE1 methyl ester)

ONO-802 was used in the form of vaginal suppositories for the termination of early pregnancy in 63 healthy volunteers. Fifty-four (86%) of the 63 cases had complete abortions and remaining 9 (14%) had incomplete abortions.One (1.6%) of the 63 cases complained of nausea and vomiting, and 3 (4.8%) complained of headaches. No other side effects were observed.These results suggest that ONO-802 is acceptable in the form of vaginal suppositories for the termination of early pregnancy.     

Cyclic nucleotide hydrolysis in the thyroid gland. General properties and key role in the interrelations between concentrations of adenosine 3':5'-monophosphate and guanosine 3':5'-monophosphate.

Phosphodiesterase activities of horse (and dog) thyroid soluble fraction were compared with either cyclic AMP (adenosine 3':3'-monophosphate) or cyclic GMP (guanosine 3':5'-monophosphate) as substrate. Optimal activity for cyclic AMP hydrolysis was observed at pH 8, and at pH 7.6 for cyclic GMP. Increasing concentrations of ethyleneglycol bis(2-aminoethyl)-N,N'-tetraacetic acid inhibited both phosphodiesterase activities; in the presence of exogenous Ca2+, this effect was shifted to higher concentrations of the chelator. In a dialysed supernatant preparation, Ca2+ had no significant stimulatory effect, but both Mg2+ and Mn2+ increased cyclic nucleotides breakdown. Mn2+ promoted the hydrolysis of cyclic AMP more effectively than that of cyclic GMP. For both substrates, substrate velocity curves exhibited a two-slope pattern in a Hofstee plot. Cyclic GMP stimulated cyclic AMP hydrolysis, both nucleotides being at micromolar concentrations. Conversely, at no concentration had cyclic AMP any stimulatory effect on cyclic GMP hydrolysis. 1-Methyl-3-isobutylxanthine and theophylline blocked the activation by cyclic GMP of cyclic GMP of cyclic AMP hydrolysis, whereas Ro 20-1724 (4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone), a non-methylxanthine inhibitor of phosphodiesterases, did not alter this effect. In dog thyroid slices, carbamoylcholine, which promotes an accumulation of cyclic GMP, inhibits the thyrotropin-induced increase in cyclic AMP. This inhibitory effect of carbamoylcholine was blocked by theophylline and 1-methyl-3-isobutylxanthine, but not by Ro 20-1724. It is suggested that the cholinergic inhibitory effect on cyclic AMP accumulation is mediated by cyclic GMP, through a direct activation of phosphodiesterase activity.     

The binding of carbon monoxide to cytochrome c oxidase.

The effect of CO on the optical absorbance spectrum of partially reduced cytochrome c oxidase has been studied. The changes at 432 and 590 nm suggest that the cytochrome alpha2/3+ - CO compound is formed preferentially and that concomitantly a second electron is taken up by the enzyme. From the CO-induced changes at 830 nm it is concluded that in the partially reduced enzyme addition of CO causes reoxidation of the copper component of cytochrome c oxidase. Addition of CO to partially reduced enzyme (2 electrons per 4 metal ions) also brings about a decrease in the intensities of electron paramagnetic resonance signals of high-spin heme iron near g = 6 and of the low-spin heme at g = 2.6. Concomitantly both the low-spin heme a signal at g = 3 and the copper signal at g = 2 increase in intensity. These results demonstrate that formation of the reduced diamagnetic cytochrome a3 - CO compound is accompanied by reoxidation of both the copper component detectable by electron paramagnetic resonance and possibly also by cytochrome a.     

Different types of mitochondria in parenchymal and non-parenchymal rat-liver cells.

1. Intact and pure parenchymal and non-parenchymal cells were isolated from rat liver. The specific activities of several mitochondrial enzymes were determined in both parenchymal and non-parenchymal cell homogenates to characterize the mitochondria in these liver cell types. 2.In general the activities of mitochondrial enzymes were lower in non-parenchymal liver cells than in parenchymal cells. The specific activity of pyruvate carboxylase in non-parenchymal cells expressed as the percentage of that in parenchymal cells was onlu 2% for glutamate dehydrogenase 4.3% and for cytochrome c oxidase 79.4%. Monoamine oxidase, as an exception, has an equal specific activity in both cell types. 3. The activity ratio of pyruvate carboxylase at 10 mM pyruvate over 0.1 mM pyruvate is 3.35 for parenchymal cells and 1.50 for non-parenchymal cells. This indicates that non-parenchymal liver cells only contain the high affinity form of pyruvate carboxylase in contrast to parenchymal cells. 4. The ratio of glycerol-3-phosphate cytochrome c reductase over succinate cytochrome c reductase activity differs from parenchymal (0.01) and non-parenchymal cells (0.10). This might indicate that the glycerol-3-phosphate shuttle, which is important for the transport of reduction equivalents for cytosol to mitochondria is relatively more active in non-parenchymal cells than in parenchymal cells. 5. The activity pattern of mitochondrial enzymes in parenchymal and non-parenchymal cell homogenates indicates that these cell types contain different types of mitochondria. The presence of these different cell types in liver will therefore contribute to the heterogeneity of isolated rat liver mitochondria in which the mitochondria from non-parenchymal cells might be considered as "non-gluconeogenic".     

Strain improvement inStreptomyces galilaeus,a producer of anthracycline antibiotics galirubins

The production of ε-pyrromycinone glycosides inStreptomyces galilaeus increased 12-fold, with respect to the wild strain, as a result of a sequential procedure including both natural selection and treatment with mutagens (nitrous acid, UV light and γ-irradiation). Nitrous acid exhibited the highest mutagenic effect, both in increasing the productivity and in inducing blocked mutants. A mutant strain blocked in the biosynthesis of glycosides and accumulating free ε-pyrromycinone as the principal metabolite was obtained.