The Biochemistry of Ferritin 203 



Amino acid analyses of apoferritin and ferritin indicate that no nitro- 

 gen components are present other than amino acids. The content of 

 dicarboxylic and basic amino acids (Table 5) agrees with the observed 



Table 5. Amino Acid Nitrogen Distribution in Apoferritin and Ferritin 



Apoferritin 



A. Mazur, I. Litt, and E. Shorr, J. Biol. Chem., 187, 473, 1950. Serine has 

 also been shown to be present. Analyses reported above were done in most 

 cases by the microbiological assay technique; several by specific colorimetric 

 methods. The total S was 0.89%, of which 98% was accounted for by the 

 cystine and methionine content. The amino N was 5.0% of the total N. 



isoelectric point for horse ferritin, 4.4, determined electrophoretically. 

 Crystalline dog ferritin has an isoelectric point of 5.2; that from the 

 human is 5.5. Evidence was obtained from quantitative immuno- 

 chemical studies 2 that these three ferritins are related but not identi- 

 cal; they cross-react, but the heterologous ferritin antigen reacts to a 

 lesser extent than the homologous ferritin with its antibody. However, 

 ferritins from different tissues of the same animal (liver and spleen) 

 appear to be immunochemically identical. 



Sulfhydryl Groups and Ferritin Activity 



Our studies attempting to relate the structure of ferritin to its bio- 

 logical activities made use of the rat test for vasodepressor effect 10 



