198 LIFE: ITS NATURE AND ORIGIN 



situations, and it appears that the new substances which the yeast 

 "learns" to ferment add their own specificity to a system of molecules 

 to make a new prosthetic group. (See also the work of T. M. Sonne- 

 born in Chapter 8.) 



(4) Deflocculation and Elution 



These may liberate carriers and/or prosthetic groups, which can 

 then become effective as gene modifiers or as catalyst formers; or 

 pre-formed enzymes may be freed from inhibitors or from an 

 inactivating adsorption. 



The Svedberg (Nobel prize, 1927) 37 and his collaborators 

 found that the molecules of the respiratory protein hemocyanin 

 from the snail Helix pomatia shows, when slightly acid (pH 6-8), 

 a molecular weight of 6,740,000; but when made slightly alkaline 

 (pH 8-0) the protein splits into three components whose molec- 

 ular weights are 6,740,000, 3,370,000, and 842,000 respectively. 

 Restoration of the pH to 6-8 causes the fragments to reunite. 

 Dissociation of proteins may follow high dilution, or the addition 

 of an amino acid or another protein. As little as 0.001 per cent 

 of thyroxin causes an appreciable dissociation of thyroglobulin. 

 The action of a dissociating compound on a protein is more or 

 less specific. Thus in the presence of ammonium chloride, argi- 

 nine dissociates serum albumin but not Helix hemocyanin, while 

 lysine plus ammonium chloride splits the latter protein but not 

 the former. Guadinine chloride affects Helix hemocyanin very 

 strongly, but serum albumin only slightly. Clupein splits both 

 proteins, but arginine, in the absence of ammonium chloride, 

 affects neither. 



Epitomizing the work on the important respiratory proteins, 

 which are interesting from a taxonomic as well as a physico-chem- 

 ical point of view, Svedberg distinguishes two groups: 



(1) Respiratory proteins active in cells: e.g., Keilin's cytochrome-C, 

 Warburg's "yellow enzyme" (now known to be of complex nature), 

 and myoglobin ("muscle hemoglobin") which takes up and gives off 

 oxygen along a dissociation curve, and seems to serve as an oxygen 

 reservoir for the organism. The first two take part in cellular oxida- 

 tion-reduction reactions. 



(2) Respiratory blood proteins, falling into the following classes: 



(a) red pigments (erythrocruorins, hemoglobins) 



(b) green pigments (chlorocruorins) 



(c) blue pigments (hemocyanins) 



(d) reddish-brown (hemerythrins) 



