Kinetic properties of pig (Sus scrofa domestica) and bovine (Bos taurus) D-fructose-1,6-bisphosphate 1-phosphohydrolase (F1,6BPase) - Liver-like isozymes in mammalian lung tissue

F1,6BPases from porcine and bovine lung were isolated and their kinetic pro perties were determined, K-s, K-is and beta were determined assuming partia l-noncompetitive inhibition (simple intersecting hyperbolic noncompetitive inhibition) of the enzyme by the substrate. Values for K-s were 4.1 and 4.4 mu M for porcine and bovine F1,6BPase, respectively and values for beta we re close to 0.55 in both cases. K-is were 9 and 15 mu M for porcine and bov ine F1,6BPase, respectively. I-0.5 for AMP were determined as 7 mu M for pi g enzyme and 14 mu M for F1,6BPase from bovine lung. The enzymes were inhib ited by F2,6BP with K-i's of 0.19 and 0.21 mu M for porcine and bovine enzy mes, respectively. In the presence of AMP concentration equal to I-0.5, the K-i values for pig and bovine enzymes were 0.07 and 0.09 mu M, respectivel y. The levels of F2,6BP, AMP and antioxidant enzymes activities in pig and bovine lung tissues were also determined. The cDNA coding sequence of pig l ung F1,6BPase(1) showed a high homology with pig liver enzyme, differing on ly in four positions (G/C-63, T/A-808, G/C-884 and T/A-1005) resulting in a single amino acid substitution (Gly-295 for Ala-295). It is hypothesized t hat the lung F1,6BPase participates in gluconeogenesis, surfactant synthesi s and antioxidant reactions. (C) 2000 Elsevier Science Inc. All rights rese rved.