Aqueous micelles are capable of solubilizing organic molecules with quite distinct polarities and degrees of hydrophobicity. Experimental Ks values for incorporation of neutral solutes in anionic sodium dodecyl sulfate micelles (SDS; 66 solutes), cationic hexadecyltrimethylammonium (CTAB; 42 solutes) and dodecyltrimethylammonium bromide micelles (DTAB; 39 solutes), and nonionic Brij-35 micelles (19 solutes) exhibited excellent fits (multiple correlation coefficients >0.98; standard deviations <0.2) to the linear solvation free energy relationship (LSER) proposed by Abraham (Chem. Soc. Rev. 1993, 22, 73): log Ks = c + -2 + ¿ /L + sn2 + rR2 + v(Vx/100). The LSER is based on medium-independent parameters for solute hydrogen bond acidity ( 2) and basicity ( ß ), excess molar refraction (R2), dipolarity ( 2), and volume (Vx). For all four detergents, incorporation is dominated by the Vx terms (positive, reflecting the hydrophobic effect) and the ß terms (negative, implying that bulk water is a better hydrogen bond donor than the micellar solubilization site). The contributions of 2 and /?", though smaller, vary in a chemically satisfying manner with detergent charge and stmcture. Incorporation is relatively insensitive to the solute dipolarity 2. These LSERs appear to provide a convenient framework for understanding the factors which contribute to the micellar solubility of organic solutes and for developing quantitative structure-solubility relationships for organized media.

Despite the intense interest in the metabolic regulation and evolution of the ATP-producing pathways, the long standing question of why most multicellular microorganisms metabolize glucose by respiration rather than fermentation remains unanswered. One such microorganism is the cellulolytic fungus Trichoderma reesei (Hypocrea jecorina). Using EST analysis and cDNA microarrays, we find that in T. reesei expression of the genes encoding the enzymes of the tricarboxylic acid cycle and the proteins of the electron transport chain is programmed in a way that favors the oxidation of pyruvate via the tricarboxylic acid cycle rather than its reduction to ethanol by fermentation. Moreover, the results indicate that acetaldehyde may be channeled into acetate rather than ethanol, thus preventing the regeneration of NAD ؉ , a pivotal product required for anaerobic metabolism. The studies also point out that the regulatory machinery controlled by glucose was most probably the target of evolutionary pressure that directed the flow of metabolites into respiratory metabolism rather than fermentation. This finding has significant implications for the development of metabolically engineered cellulolytic microorganisms for fuel production from cellulose biomass.Evolution has produced a diverse array of metabolic pathways and regulatory mechanisms that reflect the adaptation of an immense variety of microorganisms to different environments and nutritional requirements. A prominent example is the metabolism of glucose, the primary and preferred fuel for eukaryotic microorganisms. Although glucose is metabolized by a highly conserved series of connected enzymatic reactions, the mechanisms that regulate its fate and the properties of the ATP-producing pathways have been subjected to selection pressure during evolution. Aerobic (respiration) and anaerobic (fermentation) pathways are used by microorganisms to obtain energy from glucose, in the form of ATP. These pathways allow organisms to produce ATP at different rates and with different efficiencies; respiration proceeds at a lower rate and with a high yield, whereas fermentation operates at higher rates but with lower yield. Selection pressure imposed by energy limitation and the high ATP yield of respiration has been implicated in facilitating the evolutionary transition from unicellular to undifferentiated multicellular organisms (1).Unicellular microorganisms, such as the yeast Saccharomyces cerevisiae, use both pathways depending on the metabolic state of the cell, whereas multicellular microorganisms, such as filamentous fungi, preferentially use respiration (2). Mucor racemosus, a dimorphic fungus that can grow either in a unicellular (yeast-like) or a multicellular (mycelial) form, also uses both; the unicellular form exploits fermentation, whereas the multicellular form is capable of respiration (3-5).S. cerevisiae preferentially ferments glucose, even in the presence of oxygen, producing ethanol and CO 2 by anaerobic metabolism. Only after exhaustion of the available glucose...

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Oxygen is essential for the survival of obligatorily aerobic eukaryotic microorganisms, such as the multicellular fungus Trichoderma reesei. However, the molecular basis for the inability of such cells to survive for extended periods under anoxic conditions is not fully understood. Using cDNA microarray analysis, we show that changes in oxygen availability have a drastic effect on gene expression in T. reesei. The expression levels of 392 (19.6%) out of 2000 genes examined changed significantly in response to hypoxia, transient anoxia, and reoxygenation. In addition to modulating many genes with no previously assigned function, cells respond to hypoxia by readjusting the balance of expression between genes required for energy production and consumption, and altering the expression of genes involved in protective mechanisms and signaling pathways. Moreover, we show that transient anoxia strongly represses genes for enzymes that are critical for glycolysis, and are essential for energy production under anaerobic conditions. Our study thus reveals crucial differences between the facultative anaerobe Saccharomyces cerevisiae and T. reesei with regard to the oxygen-dependent transcriptional control of the glycolytic pathway, which can account for the differential survival of the two species in the absence of oxygen.

The electronegativity equalization methodology, EEM, is frequently used to calculate the charge distribution and reactivity index (e.g., local softness and hardness, condensed Fukui function) of molecules. However, recent work (Chelli, R. et al., J. Chem. Phys. 1999, 111, 8569) has shown a serious shortcoming of EEM in the prediction of the polarizability for large molecules. In this paper, our goal is to show that we can obtain a reliable dipole moment for polypeptides in vacuum and continuum-dielectric solvent using the constrained charge approximation and the generalized Born-electronegativity equalization method. Different EEM parameterizations were tested and compared to the expected values of the dipole moment vector operator as calculated at the ab initio B3LYP/6-311G(d,p) level. One EEM parameterization (Bakowies, D., Thiel, W., J. Comput. Chem. 1996, 17, 87) when used with the constrained charge approximation and the generalized Born-electronegativity equalization method was comparable to the CM1 charge model (Storer et al., J. Comput.-Aided Mol. Des. 1995, 9, 87) in the prediction of the dipole moment vector in vacuum and continuum-dielectric solvent, but was calculated with a much greater computational efficiency.