Diamine oxidase activity in fibroblasts from normal and cystic fibrosis patients

Diamine oxidase is the initial enzyme involved in the degradation of polyamines, whose metabolism has been reported as abnormal in cystic fibrosis (CF). Diamine oxidase activity, using putrescine as substrate, was measured in homogenates of human fibroblasts cultured in vitro from normal and cystic fibrosis patients. The pH optimum of the crude enzyme was 7.8. Diamine oxidase activity per microgram protein peaked during periods of greatest proliferative rate and reached its nadir when fibroblasts grew in static (confluent) phase. No difference was found between normal and CF fibroblasts in specific activity of diamine oxidase, but CF cells exhibited a slightly lower protein content during logarithmic growth when compared with normal cells.