Mat 6, 1921] 



SCIENCE 



445 



been known. Hitherto, however, the evident 

 points of similarity which these metals pos- 

 sess have not been offered to explain their 

 singular activity in respiration. 



In the first place, as Griffiths- has pointed 

 out, the atomic weights of these metals differ 

 very slightly from one another : Mn = 55 ; 

 Cu = 53; Fe = 55.9; V = 51.^ Is such a 

 condition purely accidental, or does it indi- 

 cate something concerning the chemical 

 affinities of the proteins with which tliese 

 metals are associated? It should be noted 

 also that the valences of the elements in ques- 

 tion are variable to an unusual degree (Cu, 

 1-2; Mn, 2-7; Fe, 2-3; V, 3-5). So marked 

 a degree of variation may be without theoret- 

 ical significance, yet it is an interesting coin- 

 cidence. These metals also closely approxi- 

 mate one another in specific gravity. In ad- 

 dition they all form oxides with great facility. 

 But perhaps the most suggestive property 

 which they have in common is that of 

 catalysis. 



It is a commonplace of inorganic chemistry 

 that minute amounts of iron and of man- 

 ganese hasten many reactions. This is like- 

 wise true of both copper and vanadium. But 

 it is much more significant that these same 

 elements also have a very profound catalytic 

 effect upon many physiological processes. 

 One part of manganese in one million greatly 

 accelerates the growth rate of Aspergillus 

 niger.* Moreover, the salts of copper, iron 

 and manganese serve as powerful catalaysers 

 for peroxides, and will in some cases replace 

 the enzyme peroxidase. Bertrand" believed 

 that his enzyme " laccase " owed its activity 

 to manganese, but it was subsequently shown 

 by Bach" that iron could take the place of 



2 " Respiratory Proteids, " London, 1877, p. 60. 



3iSin<;e GriflS.th's work, vanadium has been de- 

 scribed by Henze (1911-12, Zeits. physiol. Chem., 

 72, 494; 79, 215) for the blood of ascidians. The 

 writer includes it, therefore, with the list of 

 Griffiths. 



♦ Bertrand, 0. R., Acad. Sci., Paris, 1912, 154, 

 381. 



5 C. R. Acad. Sci., Paris, 1897, 124, 1032. 



« Chem. Berichte, 1910, 43, 364. 



manganese without altering the activity of 

 " laccase."^ This latter fact serves as a 

 sti-iking parallel to the replacement of iron 

 by copper and manganese in certain of the 

 respiratory pigments. But this parallel may 

 be pushed still further. Wlien acting upon 

 peroxides, these metals are serving in the 

 capacity of catalysts. Hiow, it is not wholly 

 impossible that the respiratory metals serve in 

 the same way. 



Alsberg and Clark' believe that the copper 

 of hiemoeyanin acts as a catalyst for oxygen, 

 and if this be the case, the oxygen would be 

 more readily given off to such acceptors as 

 are present in the tissues, thus making 

 hiemocyanin in reality analogous to a per- 

 oxide-peroxidase system. As for vanadium, 

 Hecht^ holds (on the grounds of the relatively 

 low binding power for oxygen which Winter- 

 stein^" reports for ascidian blood) that vana- 

 dium, too, probably serves the role of catalyst 

 in the blood of tunicates. Also, from the 

 description which (3-riffiths^^ gives of his pin- 

 naglobin,^- it is not at all impossible that tlie 

 manganese of this pigment serves in a sim- 

 ilar capacity. The fact that the metals are 

 always present in very small quantities fur- 

 ther strengthens the catalyst hypothesis. 

 Hsemocyanin, which has a molecular weight 

 of 18.762 (Griffiths), has in its molecule only 

 63.6 gram molecules of copper. Further- 

 more, one should recall that in certain slug- 

 gish animals respiratory pigments are present 

 which are not associated with any oxidizing 

 metals. These have been investigated exten- 

 sively by Griffiths,'^^ and are called by him 

 aehroglobins. An a-achroglobin is found in a 

 limpet, Patella vulgata, and a j8-achroglobin 

 in chitons. A y-achroblobin was described for 



T Bayliss, ' ' Principles of Gen. Physiol., ' ' 1918, 

 London, p. 585. 



8 Jour. Biol. CJiem., 1914, 19, 503. 



B Amer. Jour. Physiol., 1918, 40, 165. 



loBiochem. Zeits., 1909, 19, 384. 



11 "Respiratory Proteids," London, 1897. 



12 A respiratory protein containing manganese. 

 It was first isolated from Pinna squamosa, from 

 which it derives its name. 



13 " Respiratory Proteids," London, 1897. 



