Diamine Oxidase Activity in Fibroblasts from Normal and Cystic Fibrosis Patients

Abstract

Summary: 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 μg 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.

Speculation: Aberrations in the levels of polyamines in blood, despite normal levels of polyamine biosynthetic enzymes in fibroblasts, have been reported in CF patients. No differences were found between normal and CF fibroblasts in the levels of the polyamine catabolic enzyme, diamine oxidase, suggesting that an abnormality of the oxidative deamination of polyamines, as expressed in the fibro-blast, is not the primary defect in CF. The altered blood levels of polyamines may be a secondary phenomenon found only in vivo, or may be due to an aberration of polyamine acetylation or conjugation. The establishment of normal values of diamine oxidase for different phases of growth of human fibroblasts may in the future allow comparison with fibroblasts in which a defect in polyamine catabolism is suspected.

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