Arsenate replacing phosphate – alternative life chemistries and ion promiscuity Original paper

What was studied?

This review explores the fascinating idea that arsenate might replace phosphate in biological systems, specifically in critical biomolecules such as DNA and RNA. The study evaluates the potential for arsenic-based life forms by discussing how arsenate shares chemical similarities with phosphate. The review delves into the possibility of arsenate-promiscuity in enzymes that typically utilize phosphate, including enzymes involved in phosphate metabolism. It considers the biochemical properties of arsenate and phosphate, highlighting how arsenate esters exhibit high instability compared to phosphate esters, especially in water. The research also investigates arsenate’s interaction with various enzymes and proteins, the possible replacement of phosphate in cellular structures, and the implications of such substitution for life on Earth, particularly under environments where phosphate might be scarce.

Who was studied?

The review centers around arsenate’s role in biochemical reactions, and the studies mainly involve microbial organisms that thrive in environments rich in arsenic. This includes research into bacteria such as Halomonadaceae GFAJ-1, which can potentially substitute arsenate for phosphate in its DNA. The review discusses the biochemical assays performed on enzymes like L-aspartate-β-semialdehyde dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, and purine nucleoside phosphorylase, all of which were tested with arsenate as a substitute for phosphate. The study also includes comparisons with phosphorus-dependent organisms and their enzymes, analyzing the promiscuity of these proteins for arsenate and phosphate, and how this affects enzymatic activity and the stability of metabolic processes.

Most important findings

The study presents significant findings regarding arsenate-phosphate promiscuity in enzymes. Several enzymes that typically utilize phosphate as a substrate, such as L-aspartate-β-semialdehyde dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase, were found to also accept arsenate as a substrate, catalyzing reactions similarly to phosphate. However, the study notes that while arsenate can replace phosphate in some enzymatic reactions, it is not as stable as phosphate, particularly in forming esters. Arsenate esters hydrolyze much more rapidly than phosphate esters, leading to futile cycles where the arsenate-containing compounds quickly break down. The review also discussed arsenic-based life forms and how arsenate’s ability to substitute for phosphate could be advantageous in environments with limited phosphorus. Nevertheless, this substitution would create challenges due to arsenate’s instability and the hydrolytic breakdown of arsenate esters. The research also highlights the evolutionary implications of arsenate-phosphate promiscuity, suggesting that organisms in arsenic-rich environments might evolve to adapt to this chemistry.

Key implications

This research suggests that while arsenate-based life remains controversial, the potential for arsenate to replace phosphate in some biochemical pathways opens new avenues for understanding alternative life chemistries. The findings underscore the need for further research into enzyme promiscuity and arsenate utilization, especially in extremophiles that may thrive in arsenic-rich environments. Understanding arsenate’s interactions with enzymes can help elucidate the biochemical constraints that limit the incorporation of arsenate into critical biomolecules like DNA. The study also has implications for bioremediation, as harnessing the ability of certain organisms to utilize arsenate instead of phosphate might help in treating arsenic contamination. Finally, the research encourages the scientific community to explore the possibility of arsenic-based life forms in environments with limited phosphorus, providing insights into astrobiology and the search for extraterrestrial life.