Molecular transformation of tumor adenylosuccinate synthetase and characteristics of its converting factor.

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.