Heme biosynthesis in the heart

The rates of biosynthesis of heme a and heme b in hearts of fed and fasted rats were measured using an isolated heart perfusion system. δ-Aminolevulinic acid synthetase activity was decreased in hearts of fasted rats to about 30% of values in hearts obtained from fed rats. [¹⁴C]Glycine incorporation into hemes a and b of cardiac tissue obtained from fasted rats was also decreased to about 30% of values obtained in hearts from fed rats. Cobalt addition to the perfusion fluid led to a decrease in cardiac δ-aminolevulinic acid synthetase activity just as cobalt administration to rats does in vivo. These studies strongly suggest that δ-aminolevulinic acid synthetase activity regulates the rate of synthesis of hemes a and b in the heart.