Characterization of cytosolic malic enzyme in human tumor cells

Cytosolic NADP(+)-dependent malic enzyme (ME) from human tumor cells was characterized in detail and compared to ME from normal human tissues produced in recombinant E. coli. Kinetic properties, size as seen in SDS gels, and HPLC elution profiles of tryptic digests of human 'normal cell' ME and NADP(+)-ME from tumor cells were identical. Thus, NADP(+)-ME found in tumor cells does not constitute a tumor-specific isoform as suggested by other studies but is identical to the 'housekeeping protein' predominantly expressed in human liver and white adipose tissue.