6.2.1.1 5 9 isoform ACS1 shows high levels of activity in a pH range of 7.0-8.0. Isoform ACS2 shows high levels of activity in a pH range of 7.5-8.5. Little activity is detected for either isoform ACS1 or ACS2 at pH levels below 5.0 or above 9.0 746504 6.2.1.1 5.5 8.5 pH 5.5: about 60% of maximal activity, pH 8.5: about 50% of maximal activity 661764 6.2.1.1 6 9.7 6.0: about 45% of maximal activity, 9.7: about 70% of maximal activity 574 6.2.1.1 6 10.5 6: about 50% of maximal activity, 10.5: about 60% of activity maximum 552 6.2.1.1 6.5 8.5 30-40% of maximal activity at pH 6.5 and 8.5 661680 6.2.1.1 6.8 8.8 about 50% of maximal activity at pH 6.8 and 8.8 554, 559 6.2.1.1 6.8 10.1 about 50% of maximal activity at pH 6.8 and pH 10.1 649463 6.2.1.1 7.3 8.1 90% of maximal activity at pH 7.3 and 8.1 554, 559 6.2.1.1 7.5 10 7.5: about 50% of maximal activity, 10.0: about 70% of maximal activity 568