THE ABSORPTION OF BOUND FORMS OF B-GROUP VITAMINS BY RAT INTESTINE

¹ Medical Research Council Unit for Cell Metabolism, Department of Biochemistry, University of Oxford; Plant protection Ltd., Imperial Chemicle Industries Ltd., Jealott's Hill Research Station, Bracknell, Berkshire
² Medical Research Council Unit for Cell Metabolism, Department of Biochemistry, University of Oxford

The rates of movement of bound forms of B-group vitamins (coenzyme A, thiamine pyrophosphate, diphosphopyridine nucleotide, flavin mononucleotide and biocytin) from the mucosal to serosal fluids has been measured in everted sacs of rat jejunum. Thiamine pyrophosphate, biocytin and flavin mononucleotide move at approximately the same rates as the free vitamin: there was no indication of active transport. The results thus resemble those obtained with free vitamins alone and suggest that these bound forms are absorbed by passive diffusion. Diphosphopyridine nucleotide, coenzyme A and, to a lesser extent, flavin mononucleotide were rapidly degraded to free forms of the vitamins. The breakdown of the pyridine nucleotide was studied in cell-free extracts of intestinal mucosa and has been shown to be due mainly to a DPN'ase type of enzyme, although a nucleotide pyrophosphorylase is also present. Some breakdown of biocytin to form free biotin was also found. Negligible breakdown of thiamine pyrophosphate was detectable under these conditions.

Note:

We wish to acknowledge the help and advice given to us by Professor Sir Hans Krebs. Thanks are also due to Miss Susan Graham for technical help. This work was aided by a grant to the Biochemistry Department from the Rockefeller Foundation. J.B.T. is indebted to the Medical Research Council for a training scholarship and to the Fellows of Queen's College, Oxford, for a Senior Hastings Scholarship.