Heme pigments concentration

The measurement of cured meat pigment concentration is based on the A540 of the nitrosyliron(II)protoporphyrin group (also known as nitrosylheme or NO-heme mol. wt. 646) in an extraction solution of 80% (final) acetone in water, taking into consideration the 70% water content of the meat sample. Hornsey (1956) established that only the pink NO-heme was extracted in 80% acetone. Heme groups from fresh meat pigments (Table F3.2.1) are not extractable in 80% acetone. However, upon acidification with hydrochloric acid, NO-heme in 80% acetone was completely oxidized to hemin. Thus, NO-heme concentrations could be expressed in equivalent ppm hemin. 

The recognition of metals as integral parts of enzyme systems has led to investigations aimed at elucidating their functional role in the catalytic process. Of the transition metals, iron has been best studied in this regard. This stems from several circumstances first, the characteristic color of the heme pigments early called attention to this element second, the concentration of iron in liver, muscle, and red cells is high, relative to the other transition elements third, the functional heme unit can be isolated with... 

Table III. Concentrations of Total Iron, Heme Iron, and Free Non-heme Iron in Treated and Untreated Meat Pigment Extract...

When heme proteins are degraded in mammals, the polypeptides are hydrolyzed to amino acids while the heme groups are freed of their iron, which is salvaged, and are converted to bilirubin. After transport to the liver, bilirubin is coupled to glucuronic acid and the conjugated bilirubin is excreted into bile as the principal bile pigment. When increased production or decreased excretion of bilirubin causes its plasma concentration to exceed 0.1-1.0 mg/dL (2-17 /rmol/L), it diifuses into tissues and... 

Nitrosamlnes - Nitrosamines depress ui vivo cytochrome P-450 concentrations and inhibit xenobiotic metabolism.Dimethyl-, diethyl-, and dipropylnitrosamlnes have recently been shown to cause the vivo accumulation of abnormal hepatic pigments.The pigment obtained with diethylnitrosamine, identified as N-(2-hydroxyethyl)protoporphyrin IX, did not detectably contain N-ethylprotoporphyrin IX. The demonstration that N-ethylprotoporphyrin IX is not a precursor of the N-(2-hydroxyethyl) derivative implies that the heme reacts with a preformed 2-hydroxyethyl moiety (S-hydroxylation of diethylnitrosamine is known to occur) or is alkylated during the oxidation of diethylnltrosamine-derived ethylene. 

Further suggestive evidence that the carboxylated porphyrins are precursors of protoporphyrin is presented in the studies in C. diphtheriae. It had been shown by Pappenheimer that on low iron the production of porphyrin as well as of diphtheria toxin excreted into the medium was high when the iron content of the medium was increased, both the excretion of porphyrin and the toxin were diminished. Studying the heme and porphyrin pigments of this organism, Rawlinson and Hale observed that on a medium low in iron, the diphtheria bacillus excreted high concentrations of coproporphyrin III at the same time that heme production was diminished. When the iron content of the medium was increased to a level sufficient to inhibit toxin and coproporphyrin production, the intracellular heme components, namely, cytochrome a and b, but not c, rose five- to ten-fold. 

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