Myoglobin irradiation

J.J. Shieh et al., Radiation chemistry of meat proteins myoglobin irradiated in frozen aqueous solutions, in C.C. Tsen and C. Li (eds ). Proceedings of International Symposium on Recent Advances in Food and Technology, Hua Shiang Hwan, Taipei, 1981, p. 277. 

An alternative application of flash photolysis to study myoglobin electron transfer kinetics has been employed by Hofifinan and co-workers 156). In this approach, the photoactive zinc-substituted derivative of Mb is mixed with an equivalent amoimt of ferricytochrome bs to form an electrostatically stabilized binary complex. Upon transient irradiation, the strongly reducing Zn-Mb intermediate is formed, and the kinetics of ferricytochrome reduction within the preformed complex can be monitored spectrophotometrically. The resulting kinetics represents a mixed-order process consistent with electron transfer both within the electrostatically stabilized complex and between the dissociated components of the complex. 

Fig. 8.23. NOESY spectrum (A) and NOE-NOESY spectrum (B) of met-myoglobin cyanide [36], The latter spectrum is obtained by pre-irradiation of the I2-CH3 signal.

Fig. 9.7. ID NOE difference experiments on met-aquo myoglobin. (A) Reference spectrum (a) and difference spectrum (b) observed upon saturation of peak g. (B) Intensity of negative/and d signals in (b) as a function of the irradiation frequency. Signal/is maximal when the irradiation frequency is on g, signal d shows a steady increase with increasing frequency [39].

Before summarizing the reactions generally occurring in proteins irradiated at low temperatures, it is instructive to review some of the major observations that have been made for certain representative proteins. Those selected for illustration are myoglobin, ribonuclease (RNase), the myofibrillar proteins myosin and actomysin, and gelatin. Wherever possible, comparisons will be made between results for fluid and frozen systems. 

Specific Activities of Proteins. The average specific activities of proteins after y-radiolysis to a dose of about 6 Mrads (except for myoglobin which was irradiated to 23 Mrads), HST labeling and acid hydrolysis were as follows ribonuclease, 0.76 0.21 lysozyme, 0.66 0.21 chymotrypsinogen, 0.76 d= 0.06 insulin, 0.18 0.06 myoglobin 0.46 0.23 CM reduced ribonuclease, 0.96 0.38 CM reduced lysozyme,... 

Normalized Specific Activities Among Native Proteins. Figure 9 shows a comparison of tritium distributions for native proteins irradiated to about 6 Mrads (except for myoglobin which was irradiated to 23 Mrads). Each bar represents the average normalized specific activity of five separate labeling experiments for ribonuclease and of two for each of the other proteins. The tritium distributions have many similarities. The activities of proline and methionine are generally high. Lysine and histidine are heavily labeled in most proteins, while threonine and serine... 

This series of CO-RMs demonstrates how the electronics of the ligand (the aHqme) can be tuned to alter the rate of the CO-release drastically. All the CO-RMs in Fig. 4 were used in myoglobin CO-release quantification assays, and were all found to release-CO without the need for irradiation. The CO-RMs were also found to thermally release CO in DMSO. These CO-RMs do not need myoglobin to induce CO-release. Complex 2 has a ti/2 of 1-2 minutes depending on concentration where as 3 had a ti/4 of 67 minutes which is considerably longer considering there isn t that much different in the structure. This demonstrates a really good way to tune a CO-RM to get difference types of CO-release. As discussed previously, different rates of CO-release are required to treat different conditions. 

Parent CO-RM 8 was the first pyrone compound to be tested in a myoglobin assay and it was unfortunately discovered that it did not release-CO in a myoglobin assay. This shows that this particular CO-RM is stable in aqueous solution and in the presence of myoglobin. It was not tested for co-release using irradiation but it is certainly possible that it could. 

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