Kinetic and equilibrium studies of acrylonitrile binding to cytochrome c peroxidase and oxidation of acrylonitrile by cytochrome c peroxidase compound I

Protection of apigenin against acrylonitrile-induced sperm and testis injury in rats: involvement of activation of ASK1-JNK/p38 signaling pathway

This study aims to clarify if apigenin (AP) could play a pivotal role in attenuating acrylonitrile (ACN)-induced sperm and testis injury by inhibiting ASK1-JNK/p38 signaling pathway. Male Sprague-Dawley rats were randomly divided into five groups: a control group (corn oil), an ACN group (ACN 46 mg kg^-1), an ACN + AP1 group (ACN + AP 117 mg kg^-1), an ACN + AP2 group (ACN + AP 234 mg kg^-1) and an ACN + AP3 group (ACN + AP 351 mg kg^-1). The ACN + AP groups were given ACN by gavage after a pretreatment with different dosages of AP for 30 min, whereas the rats in the control group received an equivalent volume of corn oil. The gavage was conducted for 6 days per week in 4 weeks. The results showed that AP reduced sperm deformity rate and DNA fragment index and attenuated the testicular injury induced by ACN. AP could also alleviate oxidative stress, downregulate ASK1-JNK/p38 signaling pathway and eventually inhibit mitochondria-mediated testicular apoptosis. In brief, AP could dampen oxidative stress thereby inhibiting testicular apoptosis mediated by ASK1-JNK/p38 signaling pathway, alleviating ACN-induced sperm and testis injury and exerting a protective effect on male reproductive system.

Apolar distal pocket mutants of yeast cytochrome c peroxidase: Binding of imidazole, 1-methylimidazole and 4-nitroimidazole to the triAla, triVal, and triLeu variants

Imidazole binding to three apolar distal heme pocket mutants of yeast cytochrome c peroxidase (CcP) has been investigated between pH4 and 8. The three CcP variants have Arg-48, Trp-51, and His-52 mutated to either all alanine, CcP(triAla), all valine, CcP(triVal), or all leucine residues, CcP(triLeu). The imidazole binding curves for all three mutants are biphasic indicating that each of the mutants exists in at least two conformational states with different affinities for imidazole. At pH7, the high-affinity conformations of the three CcP mutants bind imidazole between 3.8 and 4.7 orders of magnitude stronger than that of wild-type CcP while the low-affinity conformations have binding affinities about 2.5 orders of magnitude larger than wild-type CcP. Imidazole binding to the three CcP mutants is pH dependent with the strongest binding observed at high pH. Apparent pK(a) values for the transition in binding vary between 5.6 and 7.5 for the high-affinity conformations and between 6.2 and 6.8 for the low-affinity conformations of the CcP triple mutants. The kinetics of imidazole binding are also biphasic. The fast phase of imidazole binding to CcP(triAla) and CcP(triLeu) is linearly dependent on the imidazole concentration while the slow phase is independent of imidazole concentration. Both phases of imidazole binding to CcP(triVal) have a hyperbolic dependence on the imidazole concentration. The apparent association rate constants vary between 30 and 170 M(-1)s(-1) while the apparent dissociation rate constants vary between 0.05 and 0.43 s(-1). The CcP triple mutants have higher binding affinities for 1-methylimidazole and 4-nitroimidazole than does wild-type CcP.