MECHANISM OF VITAMIN B12 MALABSORPTION IN BLIND LOOP SYNDROME: BACTERIAL UPTAKE OF VITAMIN B12 AND STABILITY OF BINDING OF VITAMIN B12 TO GASTRIC INTRINSIC FACTOR

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Roth free vitamin B12 (B12) and B12 bound to the intrinsic factor (IF) were taken up by the microorganisms. The amount of B12 taken up in the presence of IF was fairly smaller than in the absence of IF. The stability of the B12-IF complex was influenced by the temperature as well as by pH. The bacterial uptake of B12 appeared to be favourable under the condition where the vitamin dissociated easily from IF. Moreover, when the B12-IF complex was incubated with the microorganisms, the free IF activity in the supernatant increased according to the bacterial uptake of B12. It seemed that the microorganisms took up B12 after the liberation of B12 from IF. The amount of B12 available for bacterial uptake was regulated by the rate of dissociation of the B12-IF complex as well as by the reciprocal changes in the size of the bacterial population and IF available. It is suggested that R12 malabsorption in the blind loop syndrome could be partly explained by the bacterial uptake of B12 in the presence of abundant microorganisms in the loop and by the predominant dissociation of the vitamin from IF.