Effects of lipids on the activity of ferrochelatase

Removal of lipids from submitochondrial particles or detergent-solubilized mitochondrial preparations of rat liver resulted in a 90% loss of ferrochelatase (protochemeferro-lyase, EC 4.99.1.1) activity. The addition of either a fatty acid or phospholipid restored enzyme activity; the extent of reactivation being correlated with the degree of unsaturation of the fatty acid or acyl chain and independent of the polar head group of the phospholipid, Arrhenius plots of the ferrochelatase activities of submitochondrial particles and detergent-solubilized mitochondrial preparations showed transition temperatures of 37 and 28.5 degrees C, respectively. Ferrochelatase of submitochondrial particles or detergent-solubilized preparations had an absolute requirement for Ca2+. The ferrous salt of oxalic acid, a Ca2+ chelator, was a very poor substrate for these preparations. In contrast, ferrochelatase activities of fatty acid- or lipid-supplemented acetone extracts of these preparations were not dependent on the presence of Ca2+ and ferrous oxalate served as substrate for these extracts.20