Heme, measurement

Figure 4 Redox titration of the cytochromes c in R. sulfoviridis G1 reaction centers. Upper part titration of the high potential hemes measured at 556nm-minus-535nm. The dotted line corresponds to the Nernst equation for n=l and Em= +350 mV. The continuous line corresponds to a two components approximation with Em(l)= +390 mV and Em(2)= +310 mV.

This IS used for synthesis of porphobilinogen fEq 10 24 Porphobilinogen is the key building block in the biosynthesis of pigments of life such as porphyrins, heme, and vitamin Interestmg application of porphobdiogen to synthesis of immunocomponents for the measurement of lead fPb by fluorescence polarizadon Immunoassay has been reported "... 

Inhibition of ferrochelatase in the heme pathway causes accumulation of protoporphyrin in erythrocytes (CDC 1985). Most protoporphyrin in erythrocytes (about 90%) exists as zinc protoporphyrin (ZnPP). This fraction is preferentially measured by hematofluorometers. Extraction methods measure all the protoporphyrin present, but strip the zinc from the ZnPP during the extraction process. For this reason,... 

ALAD, an enzyme occurring early in the heme pathway, is also considered a sensitive indicator of lead effect (Hemberg et al. 1970 Morris et al. 1988 Somashekaraiah et al. 1990 Tola et al. 1973). Because there is no well-defined blood lead threshold at which inhibition of ALAD does not occur, it allows measurement of the effect on the general population at environmental lead levels and does not require high exposure levels as with occupational workers (Hemberg et al. 1970). However, ALAD activity may also be decreased with other diseases or conditions such as porphyria, liver cirrhosis, and alcoholism (Somashekaraiah et al. 1990). 

A.M. Raitsimring, P. Borbat, T. Kh. Shokjireva and F.A. Walker, Magnetic field (g-value) dependence of proton hyperfine couplings obrai-ned from ESEEM measurements Determination of the orientation of the magnetic axes of model heme complexes in glassy media, J. Phys. Chem., 1996, 100, 5235. 

HRP is a hemoprotein containing photohemin IX as its prosthetic group. The presence of the heme structure gives the enzyme its characteristic color and maximal absorptivity at 403 nm.The ratio of its absorbance in solution at 403 nm to its absorbance at 275 nm, called the RZ or Reinheitzahl ratio, can be used to approximate the purity of the enzyme. However, at least seven isoenzymes exist for HRP (Shannon et al., 1966 Kay et al., 1967 Strickland et al., 1968), and their RZ values vary from 2.50 to 4.19. Thus, unless the RZ ratio is precisely known or determined for the particular isoenzyme of HRP utilized in the preparation of an antibody-enzyme conjugate, subsequent measurement after crosslinking would yield questionable results in the determination of the amount of HRP present in the conjugate. 

Elevated blood protoporphyrin IX activity resulting from lead inhibition of heme synthetase has been documented for humans and small mammals (Peter and Strunc 1983) and for many species of birds (Anders et al. 1982 Carlson and Nielsen 1985 Friend 1985 Franson et al. 1986 Beyer et al. 1988) recovery to normal levels occurs in a lead-free environment in 2 to 7 weeks. Franson et al. (1986) endorsed the blood protoporphyrin IX technique instead of ALAD as a means of measuring lead stress because of its comparative simplicity and lower cost. 

Synthetic models of myoglobin and hemoglobin are complex molecules that mimic the stereochemical properties of the protein active center [24] and have oxygen affinities similar to those measured for the protein [25-27]. The first heme model that reversibly binds oxygen (i.e. the picket-fence-oxygen complex Fe(TpivPP)(l,2-Melm)(02), shown in Fig. 3.3) was obtained in the early nine-teen-seventies by Collman and coworkers (TpivPP = tetrapivalami-nophenyl porphyrin 2-meIm = 2-methylimidazole) [18]. Research on synthetic models of the protein has led to a deeper understand-... 

The kinetics of reactions of NO with ferri- and ferro-heme proteins and models under ambient conditions have been studied by time-resolved spectroscopic techniques. Representative results are summarized in Table I (22-28). Equilibrium constants determined for the formation of nitrosyl complexes of met-myoglobin (metMb), ferri-cytochrome-c (Cyt111) and catalase (Cat) are in reasonable agreement when measured both by flash photolysis techniques (K= konlkQff) and by spectroscopic titration in aqueous media (22). Table I summarizes the several orders of magnitude range of kon and kQs values obtained for ferri- and ferro-heme proteins. Many k0f[ values were too small to determine by flash photolysis methods and were determined by other means. The small values of kQ result in very large equilibrium constants K for the... 

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