Identification and assignment of base pairs in three helical stems of Torulopsis utilis ribosomal 5S RNA and its RNase T1 and RNase T2 cleaved fragments via 500-MHz proton homonuclear overhauser enhancements

Imino proton resonances in the downfield region (10-14 ppm) of the 500-MHz 1H NMR spectrum of Torulopsis utilis 5S RNA are identified (A X U, G X C, or G X U) and assigned to base pairs in helices I, IV, and V via analysis of homonuclear Overhauser enhancements (NOE) from intact T. utilis 5S RNA, its RNase T1 and RNase T2 digested fragments, and a second yeast (Saccharomyces cerevisiae) 5S RNA whose nucleotide sequence differs at only six residues from that of T. utilis 5S RNA. The near-identical chemical shifts and NOE behavior of most of the common peaks from these four RNAs strongly suggest that helices I, IV, and V retain the same conformation after RNase digestion and that both T. utilis and S. cerevisiae 5S RNAs share a common secondary and tertiary structure. Of the four G X U base pairs identified in the intact 5S RNA, two are assigned to the terminal stem (helix I) and the other two to helices IV and V. Seven of the nine base pairs of the terminal stem have been assigned. Our experimental demonstration of a G X U base pair in helix V supports the 5S RNA secondary structural model of Luehrsen and Fox [Luehrsen, K. R., & Fox, G.E. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 2150-2154]. Finally, the base-pair proton peak assigned to the terminal G X U in helix V of the RNase T2 cleaved fragment is shifted downfield from that in the intact 5S RNA, suggesting that helices I and V may be coaxial in intact T. utilis 5S RNA.     

Co-operativity and enzymatic activity in polymer-activated enzymes. A one-dimensional piggy-back binding model and its application to the DNA-dependent ATPase of DNA gyrase

The binding of a ligand to a one-dimensional lattice in the presence of a second ("rider") ligand, which binds only to the first ligand (piggy-back binding), is studied. A model derived from this study is used to analyze the effects of co-operativity on the reaction rates of enzymes activated by polymeric cofactors that provide multiple binding sites for the enzyme. It is found that in the presence of strong co-operativity, the steady-state reaction rates of polymer-activated enzymes can be very different from the Michaelis-Menten paradigm. By adjusting the co-operativity parameters and the binding constants of the ligands, the model can generate apparent auto-catalytic enhancement by substrates at low substrate concentrations and apparent substrate inhibition at high substrate concentrations. The model is shown to be able to explain the differences in the rates of ATP hydrolysis by DNA gyrase in the presence of long versus short DNA molecules and in the presence of long DNA molecules at different gyrase to DNA ratios.     

Differential Proteolysis of Glycinin and beta-Conglycinin Polypeptides during Soybean Germination and Seedling Growth

The degradation of the major seed storage globulins of the soybean (Glycine max [L.] Merrill) was examined during the first 12 days of germination and seedling growth. The appearance of glycinin and β-conglycinin degradation products was detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of cotyledon extracts followed by electroblotting to nitrocellulose and immunostaining using glycinin and β-conglycinin specific antibodies. The three subunits of β-conglycinin were preferentially metabolized. Of the three subunits of β-conglycinin, the larger α and α′ subunits are rapidly degraded, generating new β-conglycinin cross-reactive polypeptides of 51,200 molecular weight soon after imbibition of the seed. After 6 days of growth the β-subunit is also hydrolyzed. At least six polypeptides, ranging from 33,100 to 24,000 molecular weight, appear as apparent degradation products of β-conglycinin. The metabolism of the glycinin acidic chains begins early in growth. The glycinin acidic chains present at day 3 have already been altered from the native form in the ungerminated seed, as evidenced by their higher mobility in an alkaline-urea polyacrylamide gel electrophoresis system. However, no change in the molecular weight of these chains is detectable by sodium dodecyl sulfate-polyarylamide gel electrophoresis. Examination of the glycinin polypeptide amino-termini by dansylation suggests that this initial modification of the acidic chains involves limited proteolysis at the carboxyl-termini, deamidation, or both. After 3 days of growth the acidic chains are rapidly hydrolyzed to a smaller (21,900 molecular weight) form. The basic polypeptides of glycinin appear to be unaltered during the first 8 days of growth, but are rapidly degraded thereafter to unidentified products. All of the original glycinin basic chains have been destroyed by day 10 of growth.     

Design of a system for the control of low dissolved oxygen concentrations: critical oxygen concentrations for Azotobacter vinelandii and Escherichia coli

The physiological activity of microorganisms in environments with low dissolved oxygen concentrations often differs from the metabolic activity of the same cells growing under fully aerobic or anaerobic conditions. This article describes a laboratory-scale system for the control of dissolved oxygen at low levels while maintaining other parameters, such as agitator speed, gas flowrate, position of sparger outlet, and temperature at fixed values. Thus, it is possible to attribute in dilute nonviscous fermentations all physiologic changes solely to changes in dissolved oxygen. Experiments were conducted with Azotobacter vinelandii and Escherichia coli. Critical oxygen concentrations for growth (that value of oxygen allowing growth at 97% of mu max) were measured as 0.35 +/- 0.03 mg/L for A. vinelandii and 0.12 +/- 0.03 mg/L for E. coli. These values are significantly different from the commonly quoted values for critical oxygen concentrations based on respiration rates. Because of the superior dissolved oxygen control system and an improved experimental protocol preventing CO2 limitation, we believe that the values reported in this work more closely represent reality.     

Covalent binding of (+)- and (-)-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyr ene to B and Z DNAs

Circular dichroism (CD) as well as absorption spectral measurements reveals that poly(dG-m5dC).poly(dG-m5dC) suffers more extensive covalent modification by (+)-dihydroxy-anti-epoxybenzo[a]pyrene [(+)-anti-BPDE] than its unmethylated counterpart and that the covalently attached pyrenyl moiety exhibits stronger stacking interactions with the bases in the methylated polymer as suggested by the much larger pyrenyl spectral red shifts, most likely the consequence of intercalation. Stereoselective binding properties of these polymers are evidenced by the much reduced preference for the (-) enantiomer. Modifications due to (+)-anti-BPDE on the 50 microM hexaamminecobalt induced Z DNAs are much less pronounced and much less stereoselective, with the pyrenyl spectral characteristics being distinct from those of the B form. Salt titrations on the (+)-anti-BPDE modified poly(dG-dC).poly(dG-dC) and poly(dG-m5dC).poly(dG-m5dC) indicate much reduced cooperativity on the B to Z transition when compared to the unmodified counterparts. Evidence also suggests that covalent modification by anti-BPDE inhibits the B to Z conversion of base pairs in its immediate vicinity, presumably through intercalative stabilization of the B conformer at high salt. In contrast to stabilizing the B conformation for the proximal base pairs, covalent lesion by (+)-anti-BPDE appears to destabilize distal base pairs with the consequence of kinetic facilitation of B to Z transformation for these regions. Interesting differential effects on the reverse Z to B transforming abilities of these two enantiomers are observed with the covalent binding of the (-) isomer showing higher potency for inducing such conversion.     

Mechanism of bleomycin: evidence for 4'-ketone formation in poly(dA-dU) associated exclusively with free base release

Incubation of poly(dA-[3'-3H]dU), poly(dA-[5'-3H]dU), or poly(dA-[5'-3H]dT) under a variety of conditions with activated bleomycin resulted in the production of free nucleic acid base, base propenal, and a small amount of 3H2O. Adjustment of the terminated reaction mixture to pH 10 and incubation at 95 degrees C resulted in a time-dependent increase in 3H2O to an amount equal to the amount of free base. If the terminated reaction mixture was incubated with NaBH4 prior to the heat and alkaline treatment, the release of 3H2O was significantly inhibited. These results are consistent with the generation by activated bleomycin of a 4'-ketone yielding free base, with the exchange of the 3'- and 5'-hydrogens by enolization and with the alkaline-induced strand scission occurring from this intermediate.     

Electrostatic interactions in sperm whale myoglobin. Site specificity, roles in structural elements, and external electrostatic potential distributions

The electrostatic free energy contribution to the stability of sperm whale ferrimyoglobin was evaluated according to the static accessibility modified Tanford-Kirkwood model. The electrostatic free energy contribution of each distinct structural element was divided into one term arising from interactions between it and other elements (interelemental) and another from interactions within the particular element itself (intraelemental). At pH 7 the majority of the terms were found to be stabilizing. The interelemental terms are the dominant ones for most structural elements. The small interelemental terms of the C and D helices are compensated by large intraelemental interactions which stabilize these short helices. Perturbations in pH can be accommodated by the structural elements through a redistribution of stabilizing and destabilizing interactions. The electrostatic potentials calculated at the surface of the protein indicate that the internal compensation of local potentials achieved during folding results in a generally neutral protein-solvent interface save for two distinct areas of nonzero potential. The accessibility of each charged atom to solvent was analyzed in terms of the surface area lost to charged, polar and nonpolar atoms separately. The net solvent accessibility lost parallels closely that lost to nonpolar atoms alone, indicating a specific role for nonpolar atoms in defining dielectric shielding of charged atoms, aside from their participation in the well-known hydrophobic interactions.     

Effects of p,p''-DDT on the Rat Brain Concentrations of Biogenic Amine and Amino Acid Neurotransmitters and Their Association with p,p''-DDT-Induced Tremor and Hyperthermia

Male, Fischer strain 344 adult rats were given various doses (25-100 mg/kg) of p,p'-DDT by oral gavage, and levels of biogenic amines, their metabolites, and amino acid neurotransmitters, tremor activity, and rectal temperature were measured at several intervals (2, 5, 12, and 24 h) after dosing. Dose-related increases in rectal temperature and in tremor activity were observed at 50-100 mg/kg 12 h after dosing. Tremorigenic doses of DDT increased the 5-hydroxyindoleacetic acid (5-HIAA) level in hypothalamus, brainstem, and striatum, whereas doses of 75 and 100 mg/kg increased the 3-methoxy-4-hydroxyphenylglycol (MHPG) level in hypothalamus and brainstem and the 3,4-dihydroxyphenylacetic acid level in striatum. Six amino acids were assayed in the brainstem, hypothalamus, and striatum; aspartate and glutamate levels were increased only in brainstem at 25-100 mg/kg. No consistent changes in concentrations of taurine, glutamine, glycine, or gamma-aminobutyric acid were observed in any of the regions assayed. Time-related increases in rectal temperature were seen 2-12 h after dosing, and the presence of tremor was observed 5-12 h after dosing; for both the time of peak effect was at 12 h. The DDT-induced hyperthermia and tremor were associated with dose- and time-related increases in levels of 5-HIAA, MHPG, aspartate, and glutamate. It is suggested that an increase in the turnover rate of 5-hydroxytryptamine (5-HT) may be responsible for the DDT-induced hyperthermia, whereas increases in the metabolism of 5-HT and norepinephrine may be involved in the tremor.     

中国人ε珠蛋白基因5′侧序列中多态性Hinc Ⅱ位点的进一步研究

本文进一步研究了我国不同民族的正常个体以及β地中海贫血患者θ珠蛋白基因5′侧序列中的多态性HincⅡ位点及其遗传性质。在广西壮族正常个体和β地中海贫血纯合子中,该多态性位点的发生频率均为75％,与正常汉族人测得值相近。家系分析资料表明,该多态性位点完全按照孟德尔规律进行遗传。     

Regulation of substrate oxidation in isolated myocardial cells by beta-hydroxybutyrate

The role of ketone bodies in myocardial substrate oxidation was examined using freshly isolated Ca2+-tolerant heart myocytes, beta-hydroxybutyrate (beta OHB) inhibited lactate oxidation by the myocytes by 30-60%, and the inhibition was concentration dependent. Palmitate oxidation was also markedly decreased, whereas octanoate oxidation was only minimally affected by the presence of beta OHB. Lactate, octanoate, or palmitate had little, if any, effect on beta OHB oxidation. beta OHB oxidation was reduced by 22-28% in myocytes isolated from chronically diabetic rats, whereas the oxidation of palmitate remained similar to the controls. However, beta OHB still inhibited palmitate oxidation to the same extent as in the control cells. Our data support the role of beta OHB as a physiologic regulator of myocardial substrate metabolism.