Thyroid function and trisomy 21. TSH increase and rT3 deficiency

An excess of thyrotropin (TSH) with normal levels of tetraiodothyronine (T4) and of 3,5,3'-triiodothyronine (T3) was confirmed in the serum of 78 trisomy 21 children. A severe deficiency of 3,3',5'-triiodo-thyronine (rT3 or reverse T3) was observed and the decrease of the rT3/TSH ratio was highly significant. These new facts suggest that the rT3 deficiency plays a peculiar role in trisomy 21 (maybe through the regulation of one or few steps of monocarbons' metabolism). A systematic control of thyroid function (including the patient's rT3 level) is mandatory for the follow-up of every trisomy 21 patient.     

Steroid-binding site of human and rabbit sex steroid binding protein of plasma: fluorescence characterization with equilenin

The interaction of the estrogen d-3-hydroxy-1,3,5(10),6,8-estrapentaen-17-one (equilenin) with the human and rabbit sex steroid binding proteins (hSBP and rSBP, respectively) has been investigated by using fluorescence and absorption spectroscopy. Equilenin competes for the binding of 5 alpha-dihydrotestosterone. The calculated binding constant of equilenin for rSBP is 1.9 X 10(7) M-1 at 4 degrees C, which can be compared with the binding constant of 5.7 X 10(7) M-1 reported for hSBP [Ross, J.B.A., Torres, R., & Petra, P.H. (1982) FEBS Lett. 149, 240]. The results of fluorescence quenching experiments with the collisional quenchers KI and acrylamide indicate that the bound steroid has limited accessibility to the bulk solvent and that there are no anionic surface groups near the steroid-binding site. The fluorescence excitation spectra of SBP-equilenin complexes are similar to the absorption spectra of equilenin in low-dielectric solvents. The fluorescence emission of the SBP-equilenin complexes, however, exhibits wavelength shifts (red shifts) opposite to those of the steroid in low-dielectric solvents or complexed with beta-cyclodextrin (blue shifts) but similar to the red shift produced by addition of the proton acceptor triethylamine to equilenin in cyclohexane. These data indicate that the steroid-binding site of hSBP and rSBP is a nonpolar cavity containing a proton acceptor that participates in a specific interaction, possibly a hydrogen bond, with the 3'-hydroxyl group of the bound steroid.     

Alterations in sex steroid-binding protein (SBP), corticosteroid-binding globulin (CBG), and steroid hormone concentrations during pregnancy in rhesus macaques

Temporal relationships between concentrations of sex steroid-binding protein (SBP), corticosteroid-binding globulin (CBG), total and free estradiol, total and free testosterone, cortisol, and progesterone were studied in plasma obtained at 1- to 3-day intervals throughout gestation in six rhesus macaques. Concentrations of SBP and CBG were measured by diethylaminoethyl cellulose filter assays. Total and free steroids were estimated by radioimmunoassay and ultrafiltration dialysis, respectively. We found that SBP was elevated between days 30 and 50 and CBG between days 60 and 140; both then declined until term (167 days). Estradiol increased gradually throughout gestation. Testosterone was elevated between days 10 and 40, then declined, and rose slightly in late gestation until approximately 15 days before delivery, when it increased markedly. Free estradiol and testosterone increased dramatically before parturition. Progesterone was elevated between days 25 and 45 and declined to relatively constant levels thereafter. Cortisol was essentially unchanged throughout gestation. Our data show that in the pregnant rhesus, levels of SBP and CBG vary independently of one another, but both decline before term; concentrations of both total and free estradiol and testosterone increase markedly before parturition; in late gestation, elevated estrogen is not associated with increased levels of SBP or CBG (as it is in human females).     

Molecular characterization of the sex steroid binding protein (SBP) of plasma. Re-examination of rabbit SBP and comparison with the human, macaque and baboon proteins

Physico-chemical characterization of the sex steroid-binding protein, SBP, of rabbit plasma reveals that it is a dimer of mol. wt 85,800 composed of similar subunits of mol. wt 43,000. These data confirm our original proposal for a dimeric structure. The protein contains 9% carbohydrate, comprised of mannose, galactose, N-acetylglucosamine and sialic acid. It is devoid of N-acetylgalactosamine and fucose. The protein binds one molecule of 5 alpha-dihydrotestosterone per dimer with a Kd of 0.89 nM (12 degrees C). Comparison with the human, monkey and baboon SBPs indicates that all these proteins have the same dimeric molecular organization and exhibit microheterogeneity in SDS-PAGE and isoelectricfocusing. Rabbit SBP, however, contains less carbohydrate and has a higher polypeptide molecular weight than all the other SBPs. Spectrophotometric data also indicate that some tryptophan residues are in a different chemical environment than those in other SBPs. The observed microheterogeneity in all four SBP species is due for the most part to variable glycosylation of the subunit and variability at the amino-terminal region of the subunit. Combination of these and other phenomena will generate a significant number of isomeric forms of the SBP subunit which will then interact stoichiometrically to yield active dimeric SBP molecules. These differ slightly from each other depending upon the charge and size of the subunit comprising the dimeric structure, and will result in the observed microheterogeneity of pure SBP preparations. Based on these results along with more recent amino acid sequence data, we conclude that all four SBPs are dimers composed of identical polypeptide chains.     

Isolation and Characterization of a Virus Inhibitor from Spinach (Spinacia oleracea L.)

A virus inhibiting protein (VI) was isolated from spinach (Spinacia oleracea L.). The VI inhibited infections of test plants with plus- and minus-strand RNA viruses. Inoculation of both local lesion and systemic hosts with TMV in the presence of varying amounts of the VI resulted in typical dose response curves for the number of local lesions or the amount of virus respectively. The lowest concentration of VI leading to a significant reduction in the number of local lesions was 0.06 μg/ml. The VI was found to inhibit local lesion formation only when applied within 2–3 h p.i. but still reduced the number of local lesions when applied up to 9 h prior to virus inoculation. The antiviral activity could be attributed to a protein of molecular weight 29,000 dalton with an isoelectric point of 10.3. Its activity was destroyed by heating for 30 min to 70°C. These characteristics resemble those of other virus inhibiting proteins described for members of the order Caryophyllales such as the Phytolacca inhibitor against which a serological relationship was obtained.     

A new lectin from tulip (Tulipa) bulbs

A lectin was isolated from tulip (Tulipa) bulbs by affinity chromatography on fetuin-agarose and partially characterized. The tulip lectin is a tetrameric protein composed of four identical subunits of M_r 28 000, which are not held together by disulphide bonds. It is not glycosylated and has an amino-acid composition typified by a high content of asparagine-aspartic acid, leucine, glycine and serine. Tulip lectin agglutinates human red blood cells, but has a much higher specific activity with rabbit erythrocytes. In hapten-inhibition assays with the latter type of red blood cell the lectin exhibits a complex specificity, whereas its agglutination with human erythrocytes is readily inhibited by N-acetylgalactosamine, lactose, fucose and galactose.Abbreviations DEAE diethylaminoethyl - PBS phosphate-buffered saline - TL Tulipa lectin - M_r relative molecular mass - SDS-PAGE sodium dodecyl sulphate-polyacrylamide gel electrophoresis     

Mode of interference of chlorosis-inducing herbicides with peroxisomal enzyme activities

In rye leaves ( Secale cereale L. cv. Petkus "Kustro") bleached in the presence of the chlorosis-inducing herbicides aminotriazole, haloxidine, San 6706 or difunone in white light of 54.2 W m^-2 (5000 lx), catalase activity was very low. In addition, the activities of glycolate oxidase and hydroxypyruvate reductase were strongly diminished in treatments with San 6706 and difunone. The lowering of the peroxisomal enzyme activities was observed in red, but not in blue light and did not occur after treatment with the non-bleaching pyridazinone derivative San 9785. The deficiencies of the peroxisomal enzymes did not appear to be involved in the initiation of the chlorosis. Instead they are probably produced as secondary consequences of the bleaching. Low peroxisomal enzyme activities were also obtained without herbicide treatment by growing the leaves in an atmosphere of 2% O₂ and 3% CO₂, but in this case were not accompanied by an increased sensitivity of the Chl to photooxidative bleaching. The peroxisomal enzymes reached as high activities as in untreated controls when the herbicide-treated leaves were grown at a low light intensity of 0.106 W m^-2 (10 lx). After transfer of herbicide-treated leaves grown under 0.106 W m^-2 to 306 W m^-2 (30 000 lx), catalase was strongly inactivated, even at 0°C. In treatments with San 6706 and difunone the increase of the activities of glycolate oxidase and hydroxypyruvate reductase was either stopped, remaining unchanged, or the enzymes were slightly inactivated after exposure to 306 W m^-2 (30 000 lx). The observations suggest that the inactivation of peroxisomal enzymes results from photooxidative events in the chloroplasts.