Studies on the Combination of Iron With Certain Proteins,Amino Acids and Related Compounds. ∗

Abstract

The present work is a continuation of the studies which have been carried out in this laboratory on the mode of combination of proteins with the inorganic elements. Previous reports have dealt with the compounds of proteins with the alkali metals 1 and with the alkaline earth elements. 2 This work has now been extended to include the compounds which ferric iron forms with certain proteins, amino acids and related substances.

The method employed consists in adding the substances to be tested to a known solution of ferric iron. To this a standard amount of ammonium thiocyanate is added and the reaction is adjusted to a definite pH. The color of this solution is compared with a standard iron thiocyanate solution. If the substance tested forms a compound with iron (e. g., complex ions) which is less dissociated than ferric thiocyanate, the color of the solution will be less intense than the standard. If the ferric compound is dissociated to a greater extent than ferric thiocyanate, no appreciable effect on the color will be noted.

The results showed that at pH 2.5 substances which possess a hydroxyl group alpha to a carboxyl group markedly reduce the color of ferric thiocyanate. The effect is less pronounced when the hydroxyl group is in the beta position. Dicarboxylic acids, which may be considered as hydroxy acids, show some effect. Hydroxy acids which contain a double bond oxygen (=0) and hydroxy groups in an arrangement such as occurs in phosphoric acid, arsenic acid and sulfuric acid markedly reduce the color of ferric thiocyanate. Casein and gelatin likewise exhibit this property. Substances which contain only hydroxyl groups (glycerine, borates, etc.) showed within the limits of concentration tested, no effect.