On Dec. 2, 2010, NASA held a press conference to announce a new form of life had been discovered — bacteria with a molecular DNA structure based on the element arsenic instead of phosphorus, an element previously thought essential for life.
But almost immediately, there was skepticism among the scientific community, questioning whether an element poisonous to most life could in fact be one of its building blocks.In January’s issue of the journal Biochemistry, Dr. Ronald Viola, UT Distinguished University Professor of Chemistry, and Dr. Dan Tawfik of the Weizmann Institute of Science in Israel explore the possibilities of the compound arsenate replacing phosphate in biomolecules and advise not dismissing too quickly the possibility of arsenic-based life.
According to Viola, the supporting data for the research NASA announced are slim.
“While there is evidence of the compound arsenate in the study, there is also evidence of the compound phosphate. There’s no direct evidence the arsenate has taken the place of the phosphate molecule in the organism’s DNA structure,” Viola said.
But the pair argue that questions about the NASA announcement shouldn’t eliminate the notion of arsenic-based life, but instead should promote new research into the element’s place in biochemistry.
“At the center of the debate is whether arsenic, which has a similar chemical structure to phosphorus, can be substituted for each other among some organisms,” Viola said.
“For this interchange to occur, organisms would need to develop extremely selective enzymes to detect the differences between arsenic- and phosphorus-based compounds.”
Viola and Tawfik said that the “promiscuity” or willingness of organisms to accept different compounds on which to build “generally provides the starting points for the evolution of new protein functions.”
“The notion of life without phosphate might be proven wrong, but life with arsenate presents extreme challenges as well as intriguing research opportunities,” Viola and Tawfik wrote.
The biggest challenge that must be overcome is the low stability of arsenate compounds, which is especially critical when the integrity of an organism’s genetic information must be maintained.
“The study of the structural, functional and evolutionary aspects of arsenate-phosphate discrimination and of the mechanisms for the discrimination of similar ions may therefore yield key insights into the possibilities of alternative life chemistries,” the researchers wrote.