H. Baker et al., HOLOTRANSCOBALAMINS IN B-12 AND NON B-12 REQUIRING PROKARYOTES AND EUKARYOTES, Comparative biochemistry and physiology. B. Comparative biochemistry, 113(4), 1996, pp. 707-709
Transcobalamins, vitamin B-12 binding proteins, deliver Bit to cell su
rface receptors which then permit B-12 to cross cell membranes for met
abolic use. There is little documentation concerning B-12 binding prot
eins in bacteria and protists. We found that prokaryotes and eukaryote
s requiring B-12, as well as those protists synthesizing B-12, also pr
oduce several transcobalamins for functionally transporting B-12 Simil
ar to humans.