PubMed · 4745713
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S L Lin, J C Chan. 1973. Urinary bicarbonate: a titrimetric method for determination.. https://doi.org/10.1016/s0009-9120(73)80028-1
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Peroxynitrite, a biological oxidant formed from the reaction of nitric oxide with the superoxide radical, is associated with many pathologies, including neurodegenerative diseases, such as multiple sclerosis (MS). Gout (hyperuricemic) and MS are almost mutually exclusive, and uric acid has therapeutic effects in mice with experimental allergic encephalomyelitis, an animal disease that models MS. This evidence suggests that uric acid may scavenge peroxynitrite and/or peroxynitrite-derived reactive species. Therefore, we studied the kinetics of the reactions of peroxynitrite with uric acid from pH 6.9 to 8.0. The data indicate that peroxynitrous acid (HOONO) reacts with the uric acid monoanion with k = 155 M(-1) s(-1) (T = 37 degrees C, pH 7.4) giving a pseudo-first-order rate constant in blood plasma k(U(rate))(/plasma) = 0.05 s(-1) (T = 37 degrees C, pH 7.4; assuming [uric acid](plasma) = 0.3 mM). Among the biological molecules in human plasma whose rates of reaction with peroxynitrite have been reported, CO(2) is one of the fastest with a pseudo-first-order rate constant k(CO(2))(/plasma) = 46 s(-1) (T = 37 degrees C, pH 7.4; assuming [CO(2)](plasma) = 1 mM). Thus peroxynitrite reacts with CO(2) in human blood plasma nearly 920 times faster than with uric acid. Therefore, uric acid does not directly scavenge peroxynitrite because uric acid can not compete for peroxynitrite with CO(2). The therapeutic effects of uric acid may be related to the scavenging of the radicals CO(*-)(3) and NO(*)(2) that are formed from the reaction of peroxynitrite with CO(2). We suggest that trapping secondary radicals that result from the fast reaction of peroxynitrite with CO(2) may represent a new and viable approach for ameliorating the adverse effects associated with peroxynitrite in many diseases.
Stoichiometric relationships for biological reactions involving intermediate formation are developed from microbial reaction fundamentals and thermodynamic principles. Biological reactions proceed through intermediates, which sequester carbon and electrons whenever their degradation is relatively slow. Modeling intermediate formation and subsequent utilization requires evaluation of the distribution of electrons, energy, and macronutrients (C and N) between energy-generating pathways and cell-synthesis pathways for each step in the mineralization of the primary electron-donor substrate. We describe how energy and electron balances are utilized to predict the stoichiometry for each step of a multi-step degradation process. Each stoichiometric relationship developed predicts substrate utilization, cell growth, and the formation of other products (e.g., H(2)CO(3) or H(+)) for one step in the pathway to full mineralization. A modeling example demonstrates how different kinetics for each step in the degradation of nitrilotriacetic acid (NTA) leads to observed patterns in experimental results, such as a delay in the release of H(2)CO(3) after NTA is removed from solution.
Regulation by irradiance level of the mechanism for dissolved inorganic carbon (DIC) acquisition was examined in the red macroalga Gracilaria tenuistipitata Zhang et Xia. For this purpose, affinity for external DIC, carbonic anhydrase (CA; EC 4.2.1.1) activity and content of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) were determined in thalli grown at 45 and 500 micromol photons m(-2) s(-1). Oxygen evolution rates declined by 50% when the medium pH was changed from 8.1 to 8.7, and the pH compensation point attained was ca. 9.2. These characteristics were unaffected by the light treatments. In contrast, photosynthetic conductance for DIC at pH 8.7 was doubled in thalli grown at high irradiance compared with those grown at low irradiance (to 0.74 x 10(-6) from 0.33 x 10(-6) m s(-1)). Photosynthetic rates at saturating DIC concentration were also higher by 60% in thalli grown at high irradiance. These differences could not be attributed to changes in the use of external DIC, since external CA activity did not vary. Although the irradiance level did not modify the pool size of Rubisco, Rubisco content expressed on a chlorophyll a basis was almost doubled at high irradiance. These results likely indicate that the internal transport of DIC towards the active-site of Rubisco, rather than the external use of DIC, is enhanced in the thalli grown at high irradiance.