Inhibition of renal ornithine decarboxylase by aminoglycoside antibiotics in vitro.
The inhibition of renal ornithine decarboxylase (ODC) by aminoglycoside antibiotics was characterized in the postmitochondrial fraction of a kidney homogenate from adult pigmented guinea pigs. Enzymatic activity was defined as the rate of decarboxylation of [14C]ornithine sensitive to a specific ODC inhibitor, alpha-difluoromethylornithine (DFMO). The Km for ornithine was 61 +/- 32 microM. There were two forms of the enzyme with respect to their affinity for pyridoxal phosphate (PLP): (I) Km = 2.1 +/- 1.8 microM; (II) Km = 36.2 +/- 12.7 microM. Putrescine, a known ODC inhibitor, acted competitively on the renal enzyme with Ki = 1.7 +/- 1.4 mM. Aminoglycoside antibiotics inhibited ODC by an uncompetitive mechanism with inhibitor constants of comparable magnitude: neomycin, Ki = 1.3 +/- 0.1 mM; gentamicin, Ki = 1.6 +/- 0.1 mM; kanamycin, Ki = 1.9 +/- 0.2 mM; and netilmicin, Ki = 1.7 +/- 0.2 mM. Neomycin inhibited both forms of the enzyme (low and high affinity for PLP) uncompetitively with similar inhibitor constants (1.5 +/- 0.3 and 1.8 +/- 0.4 mM respectively), suggesting a single mechanism of action. Inhibition of ODC suggests that aminoglycoside-polyamine interactions may be an important component of the sequence of biochemical events associated with aminoglycoside toxicity.
Henley
C M
CM
Kresge Hearing Research Institute, University of Michigan, Ann Arbor 48109.
Mahran
L G
LG
Schacht
J
J
D000617:Aminoglycosides / Q000494:pharmacology*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D009355:Neomycin / Q000494:pharmacology; D065108:Ornithine Decarboxylase Inhibitors
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D065108:Ornithine Decarboxylase Inhibitors; D009355:Neomycin