IL Chemical and Biochemical properties of a 

 new type of myoglobin in molluscs 



A. ROSSI-FANELLI, E. ANTONINI, 

 D. POVOLEDO 



Institute of Biological Chemistry, University of Rome 

 and Zoological Station, Naples 



The object of this paper is the study of a new type of myoglobin (Mb) 

 isolated and crystallized from the red buccal muscles of two common Medi- 

 terranean moUusks: Aplysia Depilans and Aplysia Limacina* The purifica- 

 tion of this pigment has been previously described. ^-^ The homogeneity of 

 crystallized Aplysia Mb was demonstrated by paper and boundary electro- 

 phoresis and by the ultracentrifuge (Fig. 1). The isoelectric point (deter- 

 mined by paper electrophoresis owing to the small quantity of material 

 available) was found to be near pH 4-5 in acetate buffer 1=0-05, 



The sedimentation constant and the diffusion rate of the pigment were 

 determined by using the Spinco Ultracentrifuge and the Perkin Elmer elec- 

 trophoresis apparatus. ^-^ The sedimentation constant S°2o was found to 

 be 2-06 xlO~^^; this is very similar to the figures obtained for myoglobin 

 of diff"erent animal species by other authors. ^-^ 



From these data it was possible to establish the molecular weight as 

 approximately 20,000; the minimum molecular weight deduced from the 

 haem content (0-30% iron) is 18,000. These values are comparable with 

 those recently found for pure and homogeneous horse Mb by Theorell and 

 Âkeson.^ The accurate spectrophotometric analysis of some derivatives of 

 Aplysia Mb (Mb+, MbOH, MbOa, MbCO, Mb) showed that both visible 

 and ultra-violet spectra of this pigment differ widely from those of mam- 

 malian Mb (see Table 2). 



The reversible combination with O2 and CO was studied with the spectro- 

 photometric method described elsewhere.' It can be seen from Fig. 2 that 

 the O2 dissociation curve of Aplysia Mb, like the mammalian Mb, is hyperbolic, 

 but the oxygen affinity is lower: P * at 20° = 2-7 mm. Hg. The Bohr effect 

 is almost absent (d log P |)/(d pH)^=0-02). The overall heat for the reac- 

 tion Mb+02->Mb02 calculated from the van't Hoff equation between 

 10° and 30° is -13-6 kcal. 



* All the properties analysed showed no significant difference between Mb obtained 

 from Aplysia Depilans and Aplysia Limacina. 



