The properties of
adenylosuccinate synthetase [
inosine monophosphate:
L-aspartate ligase (guanosine 5'-diphosphate-forming) EC 6.3.4.4]) of rat
Yoshida sarcoma ascites tumor cells changed during purification. The isoelectric points (pI) of the crude and purified
enzymes were 5.0 and 5.9, respectively. The Km values of the crude
enzyme for
inosine monophosphate,
aspartate, and
guanosine 5'-
triphosphate were calculated to be 99 +/- 1 (S.E.), 870 +/- 40, and 27 +/- 2 microM, respectively, while those of the purified
enzyme were 410 +/- 10, 980 +/- 50, and 69 +/- 5 microM, respectively. These data indicate that the crude
enzyme should be more effective for activity than the purified one. It was found that the change in pI occurred during
diethylaminoethyl cellulose column chromatography and that, during this step a compound, named pI-converting factor (ICF), was separated from the
enzyme molecule. On addition of ICF, the pI of the purified
enzyme changed from 5.9 to 5.0, indicating that the pI conversion was dependent on ICF and was reversible. ICF was nondialyzable, heat stable, and partly precipitated with 1 N
perchloric acid but was not affected by 1 N KOH. It was partially degraded by
DNAse I. These results suggest that ICF is
a DNA-like compound.