202 Essays in Biochemistry 



actions of ferritin and apoferritin when added to the antibody directed 

 against either of these proteins. 2 These findings, together with direct 

 electron microscopic studies by Farrant 8 appear to offer conclusive 

 evidence that most of the iron lies inside the protein molecule. 



Little information can be offered concerning the nature of bonding 

 of the iron micelles to the protein. However, differences between 

 ferritin and apoferritin can be demonstrated with regard to ease of 

 denaturation. As a rule globular proteins must be denatured before 

 they can be digested by pepsin or trypsin. This is also true for ferritin 

 and apofeiritin. 9 Our studies show, in addition, that ferritin is less 

 easily denatured by acid (at the same pH) than apoferritin (Table 3) 



Table 3. Effect of pH on Peptic Hydrolysis and Protein Denaturation 



Ferritin Apoferritin Hemoglobin 



determined by degree of insolubility at the isoelectric point. 



and that the greater the iron content of ferritin the less easily it is 

 denatured and, therefore, digested by pepsin (Table 4). After de- 

 Table 4. Effect of Iron Content on Peptic Hydrolysis of Ferritin 



Ferritin m S- F e Per cent 



Sample mg. N Hydrolysis 



Original 1.55 11 



Fraction A 1.04 27 



Fraction C 0.0 52 



A. Mazur, I. Litt, and E. Shorr, /. Biol. Chem., 187, 473, 1950. Fractions A 

 and C prepared from original ferritin by partial and complete removal of iron, 

 respectively, by reduction with hydrolsulfite and dialysis. 



naturation by urea-alkali, both proteins are digested by trypsin. The 

 protective effect of ferritin-bound iron against acid denaturation of 

 the protein may be due to the existence of strong bonds between the 

 iron micelles and groups within the protein which are necessary for 

 maintenance of its native state. 



