ASSIMILATION, DISTRIBUTION, AND METABOLISM OF (⁷⁵Se)-SELENITE, SELENATE, AND SELENOAMINO ACIDS BY ESCHERICHIA COLI

Abstract

Assimilation of selenium (Se) by Escherichia coli as (⁷⁵Se)-selenite, selenate, selenomethionine, selenocystine and Se‒CH₃-selenocystine revealed that (a) selenoamino acids from a culture media are more completely assimilated than selenite or selenate and (b) that the amount of selenite is assimilated three to four times selenate. Most (>95%) of the Se assimilated by E. coli could not be solubilized by sonication and ethanol extraction but much (28% to 70%) of the Se, except Se from selenomethionine, was removed by alkaline dialysis. Se from selenocystine and from Se‒CH₃-selenocystine dialyzed from intact cells, whereas Se from selenite and selenate did not. Dialyzable Se is that Se probably present in selenotrisulfide (R‒S‒Se‒S‒R) bonds or bound nonspecifically. Analysis of the soluble Se metabolites from selenite, selenate, selenomethionine and selenocystine showed that E. coli produces at least one major metabolic product common to all substrates which upon chromatography appeared to be selenocysteic acid. In monogastric animals selenite and selenate Se does not enter the primary protein structure as amino acids yet metabolites of selenite, selenate and selenocystine produced by E. coli could enter the primary protein structure of animals in minute amounts.