158 



FINE-STRUCTURE OF PROTOPLASM 



II 



oxygen bridges of cellulose from a certain degree of polymerization 

 onwards are very sensitive to oxidation, so that the chains are easily 

 degraded, for instance according to the scheme: (C6Hio05)2n -f O., 

 = 2(QHio05),0. 



Similar sensitive ether bridges may be assumed to exist in the 

 cytoplasm, so that not only too small a r^ but also too high a r^ may 

 interfere with the bonds inside a macromolecule. 



Apart from dehydrogenation, i.e., elimination of hydrogen, the 



transfer of hydrogen atoms from 

 one chain to a neighbouring chain 

 may also be responsible for bridge 

 formation. Astbury (1936) and 

 AsTBURY and Wrinch (1937) dis- 

 cuss two possibilities of bridge form 

 -ation inside folded polypeptide 

 chains of fibre proteins, and similar 

 reactions may also be considered 

 in protoplasm. The hydrogen can be 

 exchanged between neighbouring 

 keto and imido groups following 

 the lactam-lactim tautomerism ac- 

 cording to the abbreviated equation 

 > CO + HN< ^ >C(OH)-N< , 

 thus building a main valency 

 bridge. In the same way bridges 

 may be formed between keto and 

 methylene groups by keto-enol in- 

 version: > CO ^ RHC < ^ > 

 C(OH)-RC < . Such inversions 



Fig. 103. Relation between redox po- 

 tential E, hydrogen ion exponent pjj and 

 hydrogen pressure exponent r^. Abscissa : 

 PH-value of the system; ordinate: electric 

 potential E volt of the system with respect 

 to Pt-Hj-electrode (from Bladergroen, 

 1943)- 



often occur quite easily, and in many 

 cases it is impossible to decide which of the two forms is present. In 

 the case of cytoplasm, this would mean that because of the possibilities 

 discussed it would remain doubtful whether a bridge existed or not, 

 i.e., its existence might be obvious at one moment and fail at the next, 

 which would be in accordance with the great instability of the bond 

 and with the mobility of the cytoplasm. 



V. Long-range forces . Whereas the forces described under I-IV have 

 an extremely small radius of action, there are reactions between 



