B12-Vitamins and Growth of the Flagellate Ochromonas malhamensis

Abstract

The flagellate Ochromonas malhamensis requires vitamin B12 and responds only to those natural forms of the vitamin which are active also for higher animals. The relation between the rate of growth and the concentration of cyano-cobalamin is described by an equation of the form of an adsorption isotherm. The "inactive" analogues, pseudovitamin B12 and Factor A, were taken up by O. malhamensis to about the same degree as cyanocobalamin, and inhibited competitively the growth response to cyanocobalamin, apparently by blocking a cell mechanism for "binding" the vitamin.