Effect of iodide on estrogen-induced uterine peroxidase

Iodide administered in the drinking water for 5–7 days increased the activity of estradiol-induced uterine peroxidase in the immature rat. This effect was specific for iodide and could not be mimicked by chloride, bromide, thiocyanate, perchlorate or iodate. Sodium iodide also increased peroxidase activity in the parotid gland but had no effect on glucose-6-phosphate dehydrogenase in the uterus, thyroid or parotid even though estradiol produced a 2-fold increase in the activity of this enzyme in the uterus. ¹²⁵I was taken up more readily by the uterus than by muscle but this process was not influenced by prior treatment of the animals with estrogen. The in vitro effect of sulfhydryl reagents on uterine peroxidase was also investigated and proposals made for possible mechanisms of action of iodide on this enzyme in the intact animal.     

Role of methyl groups in dynamics and evolution of biomolecules

Recent studies have discovered strong differences between the dynamics of nucleic acids (RNA and DNA) and proteins, especially at low hydration and low temperatures. This difference is caused primarily by dynamics of methyl groups that are abundant in proteins, but are absent or very rare in RNA and DNA. In this paper, we present a hypothesis regarding the role of methyl groups as intrinsic plasticizers in proteins and their evolutionary selection to facilitate protein dynamics and activity. We demonstrate the profound effect methyl groups have on protein dynamics relative to nucleic acid dynamics, and note the apparent correlation of methyl group content in protein classes and their need for molecular flexibility. Moreover, we note the fastest methyl groups of some enzymes appear around dynamical centers such as hinges or active sites. Methyl groups are also of tremendous importance from a hydrophobicity/folding/entropy perspective. These significant roles, however, complement our hypothesis rather than preclude the recognition of methyl groups in the dynamics and evolution of biomolecules.     

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.     

Structural and functional variability among DQ β alleles of DR2 subtypes

Homozygous lymphoblastoid cell lines representing various Dw subtypes of DR2 were examined for polymorphism at the DQ locus by molecular and cellular techniques. The subtypes studied included Dw2, Dw12, and a group heterogenous by cellular typing that we shall refer to as non-Dw2/non-Dw12. Restriction fragment length polymorphism analysis of cell lines representing these subtypes revealed DQ -specific patterns consistent with cellular typing. Two-dimensional gel electrophoresis of DQ molecules from representative cell lines revealed a structural polymorphism of DQ among the three subtypes. The DQ chain migrated to a position that was unique to each subtype and was consistent among various representative cell lines of each subtype. Nucleotide sequence analysis of cDNA clones of DQ from Dw2, Dw12, and non-Dw2/non-Dw12 lines confirmed that the variability resided at the genetic level. Variability was found in the form of numerous scattered nucleotide substitutions throughout the first domain of these alleles. The DQ gene of the non-Dw2/non-Dw12 cell line AZH was further found to be almost identical with the DQ gene of a DR1 line (Bell et al. 1985b), implicating a common evolutionary origin of these alleles. The only difference between these two sequences was due to an apparent gene conversion event at amino acid 57. T-cell cloning experiments resulted in the derivation of Epstein-Barr virus-specific, DQw1-restricted clones that proliferated against only those cell lines that exhibited the DQ gene common to AZH and the DR1 cell line. Thus, the polymorphism among DQ alleles within DR2 results in subtype-specific restriction.     

Ethanol production from xylose by Thermoanaerobacter ethanolicus in batch and continuous culture

The fermentation of xylose by Thermoanaerobacter ethanolicus ATCC 31938 was studied in pH-controlled batch and continuous cultures. In batch culture, a dependency of growth rate, product yield, and product distribution upon xylose concentration was observed. With 27 mM xylose media, an ethanol yield of 1.3 mol ethanol/mol xylose (78% of maximum theoretical yield) was typically obtained. With the same media, xylose-limited growth in continuous culture could be achieved with a volumetric productivity of 0.50 g ethanol/liter h and a yield of 0.42 g ethanol/g xylose (1.37 mol ethanol/mol xylose). With extended operation of the chemostat, variation in xylose uptake and a decline in ethanol yield was seen. Instability with respect to fermentation performance was attributed to a selection for mutant populations with different metabolic characteristics. Ethanol production in these T. ethanolicus systems was compared with xylose-to-ethanol conversions of other organisms. Relative to the other systems, T. ethanolicus offers the advantages of a high ethanol yield at low xylose concentrations in batch culture and of a rapid growth rate. Its disadvantages include a lower ethanol yield at higher xylose concentrations in batch culture and an instability of fermentation characteristics in continuous culture.     

Effect of pH on growth and ethanol production byZymomonas

Summary In a mineral salts medium containing yeast extract, NH₄Cl and glucose (50g/L), the pH range producing the fastest growth ofZ. mobilis was 5.5–6.5 with an apparent optimum at 6.5. At constant growth rate of 0.15hr^–1, the specific rates of glucose utilization (q_s) and ethanol production (q_p) were relatively unaffected by pH over the range 7.0–5.5 but increased sharply as the pH was further decreased below 5.5 to 4.0. Under these conditions the ethanol yield was unaffected by pH over the range 4.0–6.5 but decreased markedly at pH of 7.