Hemoglobin reaction rates

Values of oxygen partial pressure in the plasmas, Ppi>m and Ppitf, can be obtained from the fraction of the total resistance resulting from the hemoglobin reaction rates ... 

Fig. 10.5 NO formation from the oxidation of N-al kyl-N -hyd roxyguan id ines in the presence of NOS. The reaction rates were assessed by a hemoglobin assay and are expressed as a percentage of those of NHA.

Some of the reactions catalyzed are very complex others are very simple. Many occur at very rapid rates. For example, nearly half the C02 produced by tissues is carried to the lungs by dissolving in the blood-stream (the rest is carried by hemoglobin). The rate of solution of C02 in water is much too slow for this process and so it is catalyzed by an enzyme called carbonic anhydrase ... 

Conformational changes could control ET reactions in proteins. The rates of such changes often are in the same range as ET rates for example, the T-R transition in hemoglobin occurs at a rate of approximately 2 X 10 s (112). Hoffman and Ratner (66,67) have pointed out that a way to test for conformational control of an ET reaction is to measure the reaction rate at different driving forces. If the rate stays the same, the ET reaction is conformationally controlled. If it does not, it is not confor-mationally controlled. No evidence for conformation control exists for ET in ruthenium-modified proteins on this basis. Data from both ruthenated His-33 in horse heart cytochrome c (126) and ruthenated His-48 in myoglobin (103) show that the rate changes with AG° in a manner consistent with Marcus theory. 

The automated method differs from the ICSH method chiefly in that oxidation and ligation of heme iron occur after the hemes have been released from globin. Therefore, ferricyanide and cyanide need not diffuse into the hemoglobin and methemoglobin, respectively. Because diffusion is rate-limiting in this reaction sequence, the overall reaction time is reduced from approximately three minutes for the manual method to 3 —15 seconds for the automated method. Reaction sequences in the Coulter S + II and the Technicon H 1 and H 2 are similar. Moreover, similar reactions are used in the other Coulter systems and in the TOA and Unipath instmments. 

Superoxide is formed (reaction 1) in the red blood cell by the auto-oxidation of hemoglobin to methemo-globin (approximately 3% of hemoglobin in human red blood cells has been calculated to auto-oxidize per day) in other tissues, it is formed by the action of enzymes such as cytochrome P450 reductase and xanthine oxidase. When stimulated by contact with bacteria, neutrophils exhibit a respiratory burst (see below) and produce superoxide in a reaction catalyzed by NADPH oxidase (reaction 2). Superoxide spontaneously dismu-tates to form H2O2 and O2 however, the rate of this same reaction is speeded up tremendously by the action of the enzyme superoxide dismutase (reaction 3). Hydrogen peroxide is subject to a number of fates. The enzyme catalase, present in many types of cells, converts... 

A total hemoglobin concentration of 0 6 to 0 8 mg/ml Is required Table III presents characteristic spectral maxima observed for the known methemoglobln variants Some methemoglobln variants vary In the rate of reaction with KCN ... 

The structural stability of mixed-metal hemoglobin hybrids also has allowed us to study low-temperature electron transfer in this system. We first reported the temperature dependence of triplet-state quenching within the [ (ZnP), Fe (H20)P] hybrids, which we attributed to the ZnP Fe P ET reaction [7d]. The rate constant dropped smoothly as the temperature was lowered from room temperature to 200 K. Below this temperature the rate constant remained roughly constant with a tunnelling rate constant of kt 9 s (Fig. 7). 

From this type of analysis, one would conclude that t must be approximately 28 for a 10% reduction in protomer to cause a 95% reduction in the nucleus concentration. This is a rather startling apparent reaction order even assuming infinite cooperativity between protomers. It is recalled that Hofrichter et al. (1974) found from a similar analysis of the rate of nucleation of human hemoglobin S (HbS) at 30 C that the apparent reaction order for the nucleation of HbS aggregation was about 32. Of course, such analyses are not fully justifiable because one may not assume ideality in the solution properties of biopolymers at high concentrations, particularly at 200 mg/ml in the case of hemoglobin. The computation for the case of tubulin polymerization does, nonetheless, emphasize that nucleation would be an especially cooperative event if only tubulin, and not ring structures, played the active role in nuclei formation. 

M. R. Luzzana and J. T. Penniston, Biochim. Biophys. Acta 396, 157 (1975) monitor the hemoglobin-Oj reaction by continuous flow combined with a Clark Oj electrode and obtain a rate profile similar to that with the spectral method. 

Carry oxygen and hemoglobin through the arteries, veins, and capillaries of living animals Used in polymer manufacture to create porosity Initiates reactions and accelerates their rate, without being consumed. Usually by means of acidic or basic properties. 

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