IN VITRO STUDIES OF THE FACTORS AFFECTING THE METABOLISM OF COBAMIDES AND COBINAMIDES BY SHEEP RUMEN MICRO‐ORGANISMS

Abstract

SummaryAn in vitro system was used to investigate the factors affecting the metabolism of cobamides and cobinamides in sheep rumen micro‐organisms.Cobalt was the primary limiting factor for the synthesis of cobamides and cobinamides in the rumen contents of sheep fed cobalt dificient rations. The vitamin B12‐activity of rumen contents from such sheep increased within two hours of cobalt addition. This rise in vitamin B12‐activity was due to an increased synthesis of 2‐methyladenyl cobamide and 5,6‐dimethylbenzimidazolyl cobamides. Other cobamides and cobinamides appeared after five hours.The addition of nitrogen bases did not affect the total rate of synthesis of cobamides in sheep rumen contents. However, in the presence of adequate cobalt the addition of certain nitrogen bases stimulated the synthesis of the corresponding cobamide at the expense of other cobamides.Rumen micro‐organisms did not synthesis significant amounts of cobamides from exogenous cobinamides. When cobinamide was added to rumen contents it was apparently converted to compounds which do not have vitamin B12‐ activity for E. coli 113–3.