Effects of metal ions on growth, β-oxidation system,and thioesterase activity of Lactococcus lactis

摘要

The effects of divalent metal ions (Ca~(2+), Mg~(2+), Fe~(2+), and Cu~(2+)) on the growth, β-oxidation system, and thioesterase activity of Lactococcus lactis were investigated. Different metal ions significantly influenced the growth of L. lactis: Ca~(2+) and Fe~(2+) accelerated growth, whereas Cu~(2+) inhibited growth. Furthermore, Mg~(2+) inhibited growth of L. lactis at a low concentration but stimulated growth of L. lactis at a high concentration. The divalent metal ions had significant effects on activity of the 4 key enzymes of the (3-oxidation system (acyl-CoA dehydrogenase, enoyl-CoA hydratase, L-3-hydroxyacyl-CoA dehydrogenase, and thiolase) and thioesterase of L. lactis. The activity of acyl-CoA dehydrogenases increased markedly in the presence of Ca~(2+) and Mg~(2+), whereas it decreased with 1 mmol/L Fe~(2+) or 12 mmol/L Mg~(2+). All the metal ions could induce activity of enoyl-CoA hydratase. In addition, 12 mmol/L Mg~(2+) significantly stimulated activity of L-3-hydroxyacyl-CoA dehydrogenase, and all metal ions could induce activity of thiolase, although thiolase activity decreased significantly when 0.05 mmol/L Cu~(2+) was added into M17 broth. Inhibition of thioesterase activity by all 4 metal ions could be reversed by 2 mmol/L Ca~(2+). These results help us understand the effect of metal ions on the β-oxidation system and thioesterase activity of Lactococcus lactis.