Aplysia myoglobin

Table 7. Conformational parameters for all residues of Aplysia myoglobin 1071...

Fig. 39. CD spectrum of Aplysia myoglobin compared to that of sperm whale myoglobin in 0.01 M phosphate buffer, pH 7.4 1071...

Denaturation of Aplysia myoglobin results in practical abolishment of the positive Cotton effect in the Soret region, indicating disappearance of the asymmetric heme environment in the denatured state (160). Analogous observations have been made on the system sperm whale ferri-myoglobin-laurylpyridinium chloride, where the heme is apparently separated to a considerable extent from the apoprotein (161). 

Pasture, A., et al. Stmctural alignment and analysis of two distantly related proteins Aplysia limacina myoglobin and sea lamprey globin. Proteins 4 240-250, 1988. 

Fig. 38. Amino acid sequence of myoglobin from Aplysia kurodai107)...

In this context, the control of O2 affinity by the distal environment of the heme group in hemoproteins can be probed by comparison of wild-type compounds with mutants which do not contain distal histidine [105]. Replacement of distal histidine by glycine results in a 10-fold decrease in O2 affinity. Within the hemoproteins themselves, the lack of distal histidine in aplysia myoblobin compared to horse myoglobin increases the dissociation rate constant by a factor of six, whereas the association rate constants are identical for both systems. The data are again consistent with the stabilization of bound O2 via hydrogen-bonding in horse myoglobin. 

Ma et alP" have analysed the pseudocontact chemical shifts of high-spin, ferrous heme in deoxy myoglobin from Aplysia limacinato determine the orientation and magnetic anisotropy of the heme prosthetic group within the heme pocket. This knowledge allowed a separation of contact and pseudocontact contributions to the chemical shifts of the heme resonances, and, from these, a mapping of spin density on the heme. 

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