Solid lactoperoxidase in the iodination ofL-tyrosine and albumin.
Solid lactoperoxidase (LP-sorbent) was prepared from lactoperoxidase and a carrier copolymer of maleic anhydride and butanediol divinylether. The properties of LP-sorbent in the iodination of tyrosine and albumin were examined. For optimizing the pH of the iodination mixture, buffers in the pH range 4.5-8.0 were used. Albumin was iodinated using Na(125)I and tyrosine using KI. The effect of substrate concentration and the sequential addition of reagents was examined in the iodination of tyrosine. The optimum pH, for iodination of albumin was 6.5 and that, for the iodination, of tyrosine 6.0-6.5. The iodination reactions were effective over a broad pH range around 6.5 resulting in almost equal iodinations. The optimum concentrations expressed as mmol/L/μmol lactoperoxidase/mg sorbent at pH 6.5 were: H2O2, 70;, KI, 64; and tyrosine, 128. The maximum catalytic activity of the LP-sorbent at pH 6.5 was 4.22 μkat/mg LP-sorbent or 28.8 kat/mol(mol of L-3-ITyr/s/mol lactoperoxidase). After the primary reaction of the LP-sorbent with hydrogen peroxide, both the supernatant and the washed solid phase exhibited iodinative activity. The iodination of tyrosine by LP-sorbent was also found to be possible in water.
Department of Clinical Chemistry, University of Helsinki, Meilahti Hospital, SF-00290, Helsinki 29, Finland.
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Karonen