Globin amino groups

Binding of C02 Most of the carbon dioxide produced in metabolism is hydrated and transported as bicarbonate ion (see p. 9). However, some CO2 is carried as carbamate bound to the uncharged a-amino groups of hemoglobin (carbamino-hemo-globin see Figure 3.7), which can be represented schematically as follows ... 

As already mentioned (see section 3.1) lipid peroxides can also break down non-enzymically to yield a variety of carbonyls, such as the hydroxyalkenals [54]. These aldehydes, and in particular 4-hydroxynonenal (HNE), can react with thiol and amino groups of nearby proteins, affecting several enzymic activities [55], These effects however appear to occur at HNE concentrations greater than 10 [lM. At low non-toxic concentrations other effects have been observed which have considerable relevance to cell proliferation. These include the stimulation of adenyl-cyclase and phospholipase C activity in liver membranes [56,57] and an inhibition of ornithine-decarboxylase activity [58] and the expression of globin genes and the protooncogene c-myc in K562 murine leukaemia cells [59]. 

Modifications of other proteins by ascorbate have been reported on the N -amino group of lysine to produce NS-(carboxymethyl)lysine which has a mass of 58amu (Dunn et al., 1990 Ortwerth et al., 1992). The mass of the difference peptide was determined using LC-MS (see Fig. 4 and Table I). The lower panel shows the spectrum of the modified peptide with a mass of 1055,2amu and the upper panel shows the spectrum of the P-globin N-terminal peptide with a mass of 983.5amu to produce a difference of 71.7amu. 

Figure 3.4 Hemoglobin transports oxygen and has a quaternary structure that shows how the chains arrange to form the molecule. As shown above, it consists of four polypeptide chains—two identical alpha globin (blue) and two identical beta globin (yellow)—each carrying a heme group (white) with a central iron atom, which bonds to oxygen. The green structure represents the amino acid glutamic acid at residue 6 on the beta chain.

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