Maize HD2, HD1-B, and HD1-A Enzyme Inhibition.: The enzyme liberats tritiated acetic acid from the substrate, which is quantified by scintillation counting. IC50 values are results of triple determinations. A 50 μL sample of maize enzyme (at 30 °C) is incubated (30 min) with 10 μL of total [3H]acetate-prelabeled chicken reticulocyte histones (2 mg/mL). Reaction is stopped by addition of 50 μL of 1 M HCl/0.4 M acetate and 800 μL of ethyl acetate. After centrifugation (1×104 g, 5 min), an aliquot of 600 μL of the upper phase is counted for radioactivity in 3 mL of liquid scintillation cocktail. MC1568 is tested at a starting concentration of 40 μM, and active substances are diluted further. NaB, VPA, TSA, SAHA, 85 TPX, HC-toxin, and tubacin are used as the reference compounds, and blank solvents are used as negative controls.