Abstract

Resonance Raman spectra of deoxy and carbonmonoxy leghemoglobin (Lb) are compared to the corresponding forms of human adult hemoglobin (HbA). It is found that the heme "core size" indicator line has nearly the same frequency for the two deoxyhemoglobins and the pi-electron density-sensitive line also falls at the same frequency. However, several other modes occur at very different frequencies in the spectra of the two proteins. From an examination of the spectrum of an HbA derivative in which the beta-carbon atoms of the heme vinyl groups were deuterated, it appears that the major differences between deoxy-HbA and -Lb may result from conformational changes in the vinyl groups. No evidence for the suggested ruffling (Irwin, M. J., Armstrong, R. S., and Wright, P. E. (1981) FEBS Lett. 133, 239-243) in deoxy-Lb was found. The spectra of carbonmonoxy-Lb and -HbA were also found to be very different. As in the deoxy case, some of these frequency differences could be attributed to vinyl group conformational differences. However, from the large difference in the pi-electron density-sensitive line, it appears that the vinyl pi-conjugation into the porphyrin in Lb(CO) may be different than it is in HbA(CO). The vinyl conformational differences may be a consequence of the looser heme pocket in Lb than in HbA. The difference in pi-conjugation could make a significant contribution to the difference in ligand binding affinity for these two globins.

Highlights

  • Resonance Raman spectra of deoxy and carbonmo- meric hemoglobinsis even greater

  • From an examinationof the spectrum of an HbA derivative in which the &carbon atomosf the heme vinyl groups were deuteratedi,t appears that the majordifferencesbetween deoxy-HbA and -Lb may result from conformational changes itnhe vinyl groups

  • Energetic importance has already beenassociated with the presence of the vinyl groups (Yonetani et al, 1974; Sono and Asakura, 1975) and their conformation could affect the extraordinarilyhigh affinity of Lb

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Summary

Resonance Raman Spectraof the Heme in Leghemoglobin

From an examinationof the spectrum of an HbA derivative in which the &carbon atomosf the heme vinyl groups were deuteratedi,t appears that the majordifferencesbetween deoxy-HbA and -Lb may result from conformational changes itnhe vinyl groups This high affinity via a large increase in oxygen on-rate (Wittenberg et al, 1972; Imamura et al 1972). From careful depolarization measurements we find that the core size marker line is at nearly the same frequenicnyLb as in HbA (ormyoglobin) This isin contrast to the resultsof Armstrong et al (1980) who reported a large differencein this. Energetic importance has already beenassociated with the presence of the vinyl groups (Yonetani et al, 1974; Sono and Asakura, 1975) and their conformation could affect the extraordinarilyhigh affinity of Lb. Striking differences betweenLbandHbAare detected in the low frequency spectra of both the deoxy and the carbonmonoxy proteins. Not all linesin each several hours with no evidence of sample degradation

RESULTS
Resonance RamSpaenctra of the Heme in Leghemoglobin
The data reported here do connoftirm previous conclusions
CONCLUSIONS
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