HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Murthy, G. K. Articles by Campbell, J. E. Search for Related Content PubMed Articles by Murthy, G. K. Articles by Campbell, J. E.

In Vitro Transformation of Inorganic Iodine to Protein-Bound Iodine in Milk by Formaldehyde

Milk and Food Research Program Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio

ABSTRACT

Addition of formaldehyde (HCHO) to raw skimmilk causes transformation of ¹³¹I^– to protein-bound iodine-131 (PB¹³¹I). Xanthine oxidase (XO) in milk oxidizes HCHO to H₂O₂ in the presence of oxygen and H₂O₂ oxidizes ¹³¹I^– to ¹³¹I₂ which binds to protein. Factors that affect XO activity, like temperature and [HCHO], affect the amount of PB¹³¹I formed. The optimum temperature for maximum PB¹³¹I formation was 65 C. Arrhenius' plot of 1/T versus log K*, the rate constant, gave activation energy of 20.92 K cal mole^–1 for the over-all reaction. Data relating 1/s and 1/v gave V_max of 93.4 ± 2.0% and K_m which varied with the rate of PB¹³¹I formation, indicating competitive inhibition type of reaction. The amount of PB¹³¹I formed, [HCHO], and XO activity were linearly correlated. The pH of milk (6.0 to 7.0) affected v but not the V_max. The optimum [I^–] oxidized at 60 C, and for 1.31 x 10^–2 M HCHO, was 2 µM per 100 ml of milk. Analysis by chromatography showed that 65 to 68% of the PB¹³¹I was in the mono-iodotyrosine, 6 to 7% in the di-iodotyrosine, 2.9 to 3.5% in the thyroxine, and 8% in the I^– form. Nonprotein constituents of milk inhibiting the XO-catalyzed reaction were removable from milk by dialysis or treatment with anion exchange resin or with activated carbon.