Acetylation of nuclear proteins in the isolated perfused rat heart

Female rat hearts were maintained by retrograde perfusion under a hydrostatic pressure of 75 cm H2O. The perfused heart had a coronary flow of 8-9 ml/min and a heart rate of 220-240 beats/min. Recirculation of [3H]acetate (2 muCi/ml perfusate) for 20 min was sufficient to label nuclear proteins. Total nuclear proteins were separated into three major classes: (1) 0.14 M NaCl soluble nucleoplasmic proteins, (2) nucleohistones and (3) nonhistone residual proteins. Approximately 88-90% of the (3H)acetate incorporated was found in the nucleohistone fraction. Polyacrylamide-urea gel electrophoresis of the histones indicated that fraction f1 was not acetylated while f3 and f2al were highly acetylated, containing 75% of the total histone radioactivity. Fraction f2b + f2a2 was moderately acetylated contributing 20-25% of the radioactivity. Nucleohistones isolated from myocardial cells showed the same percentage distribution of (3H)acetate in the histone fractions as the whole heart. Acid hydrolysis followed by steam distillation released more than 95% of the acetyl groups from the two major nucleoproteins. These data suggest that the isolated perfused heart may provide a model system to study covalent modification of nucleoproteins under controlled physiological and biochemical conditions.