Biological Properties of Model Molecules for Vitamin B₁₂

Abstract

CERTAIN tetradentate organo-cobalt complexes have physical and chemical properties which resemble those of vitamin B₁₂ (ref. 1). We have investigated whether the water-soluble complexes based on bis-(diacetylmonoximeimino)-1,3-propane—abbreviated (DOH)₂propane (Fig. 1)—will also mimic some of the biological properties of vitamin B₁₂, particularly the promotion of growth in bacteria and the catalytic function of the vitamin as a coenzyme. A vitamin B₁₂-dependent strain of Lactobacillus leichmanii was used to assay the growth stimulating properties of the (DOH)₂propane compounds, with or without added vitamin B₁₂. The growth of L. leichmanii was only irregularly stimulated when the synthetic compounds were added to the medium alone, but in the presence of catalytic amounts of vitamin B₁₂ a constant stimulation was found (Fig. 2). Each compound is active in a narrow range of concentrations, with a characteristic optimum. In the series of cobalt–aquo complexes, for example, the values are 0.07 mM for the benzyl derivative, 0.4 mM for n-propyl and phenyl derivatives, 0.7 mM for methyl and ethyl derivatives (Fig. 2a).