Heavy metal binding by hydrophobic and hydrophilic dissolved organic carbon fractions in a Spodosol A and B horizon

For a one year period intact Spodosol soil columns were percolated weekly with H₂O_deion, 1.58 mmol H₂SO₄ L^?1, and 0.79 mmol H₂SO₄ L^?1+0.64 mmol HNO₃ L^?1, respectively. Decomposition rates, soil organic carbon (OC) solubilization, dissolved organic carbon (DOC) fractions, and Cr-, Cu-, and Cd-binding by dissolved hydrophobic and hydrophilic acids were studied. Acid treatment reduced significantly OC respiration as well as OC solubilization in the humic layers. The reduced OC solubility at acid addition was more pronounced for the less polar hydrophobic compounds, resulting in a decrease of the hydrophobic acids (from ca. 65 to 40–45% of DOC), and in an increase of the hydrophilic acids (from ca. 25 to 40–45% of DOC). For B horizon leachates, DOC increased at acid treatment. Generally, hydrophobic acids were retained preferentially in the B horizon. Also in the B horizon output there was an increase of the hydrophilic acids as acidity increased (from ca. 40 to 50% of DOC). Differences between the two acid treatments were negligible. The degree of metal-organic complexes decreased in the order Cr >Cu >Cd, from A to B horizon leachates, and with increasing acidity. Hydrophilic acids were found to be the dominating ligands in complexing Cr and Cu. Actual Cr- and Cu-binding by hydrophilic acids exceeded that by hydrophobic acids 2–8 times. As the hydrophilic acids represented the most mobile DOC components in the soil columns, in particular with increasing acidity, significant amounts of Cr and Cu in the B horizon leachates were organically complexed, although a great proportion of the hydrophobic acids was retained in the B horizon.     

Acetylation by Tip60 is required for selective histone variant exchange at DNA lesions

Phosphorylation of the human histone variant H2A.X and H2Av, its homolog in Drosophila melanogaster, occurs rapidly at sites of DNA double-strand breaks. Little is known about the function of this phosphorylation or its removal during DNA repair. Here, we demonstrate that the Drosophila Tip60 (dTip60) chromatin-remodeling complex acetylates nucleosomal phospho-H2Av and exchanges it with an unmodified H2Av. Both the histone acetyltransferase dTip60 as well as the adenosine triphosphatase Domino/p400 catalyze the exchange of phospho-H2Av. Thus, these data reveal a previously unknown mechanism for selective histone exchange that uses the concerted action of two distinct chromatin-remodeling enzymes within the same multiprotein complex.