Biosynthesis of ³²P‐labelled hydroxocobalamin and a study of its behaviour in rats

Abstract

Using Propionibacterium freudenreichii and ³²P‐ATP, batches of ³²P‐labelled cobalamin (Cbl) were biosynthesized with a maximum specific activity of 61 μCi/mg, i.e. about 100 times higher than previously reported. Pharmacological doses mixed with ⁵⁷Co‐Cbl were injected subcutaneously in the form of hydroxo‐Cbl into rats subsequently killed 5–20 days later. The two labelled Cbls were distributed in approximately the same way, the highest concentration being found in kidney (typical for rats) and about one‐fifth of that in liver. These findings tallied with previous observations with radioactive cyano‐Cbl and microbiological assay. In all injected rats, the ⁵⁷Co/³²P ratio was lower in liver than in kidney. Drugs eradicating the intestinal flora had no influence. In rats receiving the vitamin orally, the ratio was higher in liver than in kidney. All of our findings could be due to formation of a cobinamide‐like compound lacking phosphorus. It is concluded that we have produced radiophosphorus‐labelled Cbl that enables studies in vivo.

• Cobalamin
• 57cobalt
• cobinamide
• 32phosphorus
• Propionibacterium freudenreichii
• vitamin B12