S-Nitrosoglutathione formation at gastric pH is augmented by ascorbic acid and by the antioxidant vitamin complex, Resiston.

CONTEXT: Exogenous nitrogen oxides must be made bioavailable to sustain normal physiology because nitric oxide synthase (NOS) deficient mice are viable. In the stomach, S-nitrosoglutathione (GSNO) is formed from ingested nitrite and high levels of airway glutathione (GSH) that are cleared and swallowed. However, gastric GSNO may be broken down by nutrients like ascorbic acid (AA) before it is absorbed. OBJECTIVE: To study the effect of AA on GSNO formation and stability. MATERIALS AND METHODS: GSH and nitrite were reacted with or without 5 mM AA or Resiston (5 mM AA with retinoic acid and α-tocopherol). GSNO was measured by reduction/chemiluminescence and HPLC. AA and reduced thiols were measured colorimetrically. O-Nitrosoascorbate and AA were measured by gas chromatography-mass spectrometry (GC-MS). RESULTS: GSNO was formed in saline and gastric samples (pH ∼4.5) from physiological levels of GSH and nitrite. Neither AA nor Resiston decreased [GSNO] at pH >3; rather, they increased [GSNO] (0.12 ± 0.19 µM without AA; 0.42 ± 0.35 µM with AA; and 0.43 ± 0.23 µM with Resiston; n = 4 each; p ≤ 0.05). However, AA compounds decreased [GSNO] at lower pH and with incubation >1 h. Mechanistically, AA, but not dehydroascorbate, increased GSNO formation; and the O-nitrosoascorbate intermediate was formed. CONCLUSIONS: AA, with or without other antioxidants, did not deplete GSNO formed from physiological levels of GSH and nitrite at pH >3. In fact, it favoured GSNO formation, likely through O-nitrosoascorbate. Gastric GSNO could be a NOS-independent source of bioavailable nitrogen oxides.

Molecular oxygen binding with alpha and beta subunits within the R quaternary state of human hemoglobin in solutions and porous sol-gel matrices.

Nanosecond laser flash-photolysis technique was used to study bimolecular and geminate molecular oxygen (O2) rebinding to alpha and beta subunits within oxygenated human adult hemoglobin in solutions and porous wet sol-gel matrices. Plasticity associated with the tertiary structure within R-state hemoglobin is explored through measurements that focus on the functional properties of hemoglobin under conditions designed to tune the tertiary structure without inducing the R to T transition. Inequivalence in the O2 binding to the alpha and beta hemes within the R quaternary structure is studied. The individual kinetic properties of the alpha and beta subunits within the hemoglobin encapsulated in sol-gels and aged as the oxy derivative are shown to be independent of proton concentration over the pH range from 6.3 to 8.5. However, buffer effects on the subunits' properties are revealed in sol-gel-free mediums. Interestingly, the alpha and beta subunits within the encapsulated hemoglobin possess the O2 rebinding properties which fall within the range of the ones for oxygenated hemoglobin in the buffer solutions. The combined results show a pattern in which there is a progression of functional properties that are ascribed to a family of conformational substates of R-state hemoglobin. O2 rebinding to the alpha and beta subunits within the oxygenated R-state hemoglobin in both solutions and wet sol-gels is revealed to be modulated by tertiary structural changes in two quite different ways. The possible structural changes, which modify the O2 rebinding properties, are discussed.