Expression and characterization of human recombinant parental and mature L-histidine decarboxylases

Human recombinant 74 kD parental (rHDC74) and 54 kD mature (rHDC54) histidine decarboxylases (HDCs) have been expressed in Sf9 cells and characterized. By immunoblot analysis, rHDC74 and rHDC54 were shown to be localized predominantly in the particulate and soluble fractions, respectively. rHDC74 exhibited histamine-synthesizing activity equivalent to that of rHDC54. An active particulate HDC was also detected in the pellets obtained from 10,000 and 100,000 g centrifugation of a cell lysate from the human basophilic leukemia cell line, KU-812-F (14 and 18% of the total activity, respectively). By four purification steps, rHDC54 was purified to homogeneity, as judged by silver staining of the SDS-polyacrylamide gel. The purified rHDC54 was eluted as a monomer form from a Superdex-200 FPLC column. The molecular mass of the enzyme was found to be approximately 54 kD on SDS-poly-acrylamide electrophoresis in the absence of 2-mercaptoethanol. Taken together, these results suggest that human HDC functions as both 74 and 54 kD forms having equivalent HDC activity, which are localized in the particulate and soluble fractions, respectively, and that the latter form exhibits its activity as a monomer form.