RT Journal Article SR Electronic(1) A1 Houde, Mario A1 Sarhan, FatheyYR 1990 T1 Localization of Vitamin B12 Binding in Euglena Gracilis JF Microbiology, VO 136 IS 3 SP 529 OP 533 DO https://doi.org/10.1099/00221287-136-3-529 PB Microbiology Society, SN 1465-2080, AB Different fractionation procedures were used to determine the location of vitamin B12 binding sites in Euglena gracilis Using uptake measurements, cell fractionation, and light and electron microscopy, the cuticle of the cell was found to be the fraction containing the majority of B12 binding sites. The apparent distribution of vitamin binding sites differed according to the cell lysis method used. The cuticle fraction was responsible for the binding of 80% of the vitamin taken up by the cell during both the rapid and the slow phase of uptake. These results suggest that vitamin B12 binding is regulated, in part, at the cuticle level, and support our previous conclusion that the secondary phase of uptake represents the synthesis of new receptor sites and not the unloading of vitamin inside the cell., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-136-3-529