Adenosine dimethylation of 16S ribosomal RNA: effect of the methylgroups on local conformational stability as deduced from electrophoretic mobility of RNA fragments in denaturing polyacrylamide gels.

The electrophoretic mobility of RNA fragments derived from the 3'-end of 16S rRNA on slabs of polyacrylamide gel in the presence of urea is strongly influenced by dimethylation of the N6-aminogroup of two adjacent adenosines. This is not due to the presence of the methylgroups per se, but must be ascribed to an effect of methylation on long range intramolecular interactions at these denaturing conditions. When it is assumed that the electrophoretic mobilities of the RNA fragments in the polyacrylamide matrix are determined by the conformational state(s) of the fragments, dimethylation of the adenosines leads in the smaller fragments to a less compact average conformation and in the larger fragments to a more compact average conformation. An effort is made to comprehend the effects of adenosine dimethylation in terms of secondary structure based on nucleotide sequence.     

Prolactin levels and the LH-response to synthetic LH-RH in the lactating sow

To determine the role of prolactin in the suppression of ovarian activity during lactation in the sow experiments were performed to investigate a possible inhibitory action of prolactin at the pituitary level. Therefore the LH-response to an intravenous injection of 25 μg synthetic LH-RH was measured in the 1st, 2nd and 3rd week of lactation. The compound was injected under high and low concentrations of prolactin in the peripheral blood, the latter achieved by removal of the piglets 6 h before administration of LH-RH. The results showed no difference in the effect of LH-RH injected at high or low prolactin levels. However, although the mean prolactin concentrations in the 1st, 2nd and 3rd week of lactation were similar, the results clearly demonstrated an increase in LH-response as lactation proceeds.The low responsiveness of the pituitary shortly post partum was also observed when the preparturient rise of prolactin was suppressed by treatment with bromoergocryptine. Injections of LH-RH in the last week of gestation given before and after the physiological increase of PRL, which occurred about 48 h before delivery, all showed low LH-response.It is obvious from the presented data that the LH-response to an intravenous injection of 25 μg LH-RH is in no way correlated with the prolactin levels at the time of treatment.     

Sister chromatid exchange induced by anti-herpes drugs.

The rate of sister chromatid exchange induced by several anti-herpes agents was measured to assess their potential mutagenicity. The agents--5-iodo-deoxyuridine (IDU), 5-trifluoromethyl-deoxyuridine (TFT), and [E]-5-(2-bromovinyl)-deoxyuridine (BVDU)--were incubated at various concentrations with human lymphocytes and fibroblasts, and that rate of sister chromatid exchanges was measured. In lymphocytes and fibroblasts BVDU and IDU did not induce exchange except at concentrations of 50 mg/l, while TFT increased the rate of exchange at a concentration of 0.5 mg/l. The rate of sister chromatid exchange is a sensitive index of chromosomal damage, and these findings provide information on the safety of some of the antiherpes agents tested. TFT increased the rate of exchange at a concentration that coincides with its minimal antiviral concentration, but BVDU did not induce exchange at therapeutic concentrations.     

Long survival in acute myelogenous leukaemia: an international collaborative study.

A group of 82 adult patients with acute myelogenous leukaemia had survived in continuous first remission for more than three years was studied. These long-surviving patients were being treated at 12 referral centres in Europe and the USA, and they were compared with other patients with acute myelogenous leukaemia from 10 of these centres. There was no clear difference in the amount of induction chemotherapy or the time taken to achieve remission. Immunotherapy was not found to improve chances of long-term survival. The 82 patients were also compared with a group of 115 patients who had no appreciable difference in the number of blood or marrow myeloblasts between these two groups at presentation, but the long survivors had significantly higher initial platelet counts and were slightly younger. The long survivors also tended to have a lower total white cell count at presentation and lower granulocyte counts; there was no obvious explanation for these differences. Eight of the 82 patients relapsed from three to four years after remission and two (of 69 patients) after four to five year. Thereafter relapse was rare, and it seems likely that some of the 40 patients who have survived for five years or more are cured.     

Studies in vitro on the involvement of O-sulphate esters in the formation of O-methylated 3,4-dihydroxybenzoic acid by rat liver.

The involvement of O-sulphate esters in the directed O-methylation was investigated in vitro with a dialysed "high-speed' supernatant from rat liver as the enzyme preparation and the catechol compound 3,4-dihydroxybenzoic acid as the substrate. The enzyme reactions involved were studied separately with the O-methylated and O-sulphated derivatives. The rate of hydrolysis by arylsulphatase was 14.5 nmol/min per mg of protein for 3-methoxy-4-sulphonyloxybenzoic acid and 10.1 nmol/min per mg of protein for 4-methoxy-3-sulphonyloxybenzoic acid. The sulphotransferase activity towards the guaiacols 4-hydroxy-3-methoxybenzoic acid and 3-hydroxy-4-methoxybenzoic acid was 570pmol of 4-O-sulphated and 350pmol of 3-O-sulphated product formed/min per mg of protein. The 3-O- and 4-O-sulphate esters of 3,4-dihydroxybenzoic acid could not serve as substrates for the catechol O-methyltransferase reaction. When either ester was incubated in the presence of S-adenosyl-L-methionine, but without the arylsulphatase inhibitor KH2PO4, 3,4-dihydroxybenzoic acid was formed, which was subsequently O-methylated in a meta/para ratio of 4.6. It is concluded that O-methylation can precede O-sulphation but that O-sulphation prevents further metabolism by O-methylation. Also O-sulphate esters do not have a directing effect on O-methylation. From the study of the simultaneous action of sulphotransferase and catechol O-methyltransferase on 3,4-dihydroxybenzoic acid we conclude that O-sulphation and O-methylation proceed independently of each other under the assay conditions used, both directed preferentially to the 3-hydroxy group.     

On the inactivity of thiol-subtilisin. The role of the intramolecular electric field

Based on computed proton affinities for several model systems, the energetics of proton transfer and the acidity of the catalytic triads Cys-His-Asn (papain). Cys-His-Asp (thiol-subtilisin) and Ser-His-Asp (subtilisin) are discussed. It is shown that in papain the ion-pair Cys--HisH+ exists owing to the intramolecular electric field, and that a similar situation is found in thiol-subtilisin. but not in subtilisin. Assuming similar reaction mechanisms for papain and thiol-subtilisin - i.e. proton transfer from HisH+ to the NH group of the scissile peptide bond - the inactivity of thil-subtilisin towards proteins is explained by the much greater basicity of His in the complex His-Asp- than in His-Asn. In order for this explanation to be consistent, it is tentatively concluded that the catalytic mechanism of the serine proteases is different from that of the cystein proteases, and involves direct transfer of the serine proton to the leaving group in the acylation step.     

Electron-microscopic immunocytochemical demonstration of separate vasotocinergic,mesotocinergic and somatostatinergic neurons in the hypothalamic magnocellular preoptic nucleus of the frog

Summary The hypothalamic magnocellular preoptic nucleus of Rana temporaria was studied at the electron-microscopic level with the use of the unlabeled antibody peroxidase-antiperoxidase complex (PAP) technique. The magnocellular preoptic nucleus of R. temporaria contains at least three different types of neurons: (1) Vasotocinergic neurons, (2) mesotocinergic neurons, and (3) neurons that contain either somatostatin or an immunologically related peptide. The present results are in complete agreement with those of previous immunocytochemical studies conducted at the light microscopic level.     

Determination of plasma theophylline by straight-phase high-performance liquid chromatography: Elimination of interfering caffeine metabolites

Several authors have recently reported interference in theophylline analysis by paraxanthine (1,7-dimethylxanthine), an important metabolite of caffeine. A method for the determination of theophylline in plasma is described, eliminating caffeine and related compounds by means of straight-phase high-performance liquid chromatography. The resulting procedure is sufficiently rapid, accurate and sensitive to be applied in routine monitoring of therapeutic levels in patients as well as for pharmacokinetic purposes. Although only 0.1 ml of sample is required, concentrations as low as 0.2 mg/l can be measured with acceptable precision. A brief comparative evaluation of this procedure with a radioimmunoassay is made.