PubMed · 115461
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N Lund, D H Lewis, J B Löfström, P A Oberg, S Odman. 1979. The MDO oxygen electrode--a sterilization problem.. https://pubmed.ncbi.nlm.nih.gov/115461/
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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.
A mathematical model of solute kinetics for the improvement of hemodialysis treatment is presented. It includes a two-compartment description of the main solutes and a three-compartment model of body fluids (plasma, interstitial and intracellular). The main model parameters can be individually assigned a priori, on the basis of body weight and plasma concentration values measured before beginning the session. Model predictions are compared with clinical data obtained in vivo during 11 different hemodialysis sessions performed on 6 patients with a profiled sodium concentration in the dialysate and a profiled ultrafiltration rate. In all cases, the agreement between the time pattern of model solute concentrations in plasma and the in vivo data proves fairly good as to urea, sodium, chloride, potassium and bicarbonate kinetics. Only in two sessions was blood volume directly measured in the patient, and in both cases the agreement with model predictions was good. In conclusion, the model allows a priori computation of the amount of sodium removed during hemodialysis, and makes it possible to predict the plasma volume changes and plasma osmolarity changes induced by a given sodium concentration profile in the dialysate and by a given ultrafiltration profile. Hence, it can be used to improve clinical tolerance to the dialysis session taking the characteristics of individual patients into account, in order to minimize intradialytic hypotension.
Tyrosine hydroxylase (TH) is the initial and rate-limiting enzyme in the biosynthesis of dopamine (DA). TH activity is significantly diminished in Parkinson's disease (PD) and by the neurotoxic amphetamines, thereby accentuating the reductions in DA associated with these conditions. Reactive oxygen and nitrogen species have been implicated in the damage to DA neurons seen in PD and in reaction to amphetamine drugs of abuse, so we investigated the hypothesis that peroxynitrite (ONOO(-)) could interfere with TH catalytic function. ONOO(-) caused a concentration-dependent inactivation of TH. The inactivation was associated with tyrosine nitration (maximum of four tyrosine residues nitrated per TH monomer) and extensive sulfhydryl oxidation. Tetranitromethane, which causes sulfhydryl oxidation at pH 6 and 8 but which nitrates tyrosines only at pH 8, inactivated TH equally at either pH. Bicarbonate protected TH from ONOO(-)-induced inactivation and sulfhydryl oxidation but increased significantly tyrosine nitration. PNU-101033 blocked ONOO(-)-induced tyrosine nitration in TH but could not prevent enzyme inactivation or sulfhydryl oxidation. Together, these results indicate that the inactivation of TH by ONOO(-) is mediated by sulfhydryl oxidation. The coincident nitration of tyrosine residues appears to exert little influence over TH catalytic function.