[Paper Review] Electron spin and the origin of Bio-homochirality I. Extant enzymatic reaction model

Wei Wang|arXiv (Cornell University)|Sep 5, 2013

Origins and Evolution of Life25 references3 citations

TL;DR

This paper proposes that electron spin polarization during enzyme-catalyzed amino acid synthesis determines biological homochirality, specifically favoring L-amino acids. Through spin filtering in chiral alpha-helices of enzymes, electrons from NAD(P)H become spin-polarized (spin-up), and according to the Pauli exclusion principle, this leads to selective formation of L-amino acids during reductive amination, offering a novel mechanism for the origin of bio-homochirality.

ABSTRACT

In this paper, I tentatively put forward a new hypothesis that the emergence of a single chiral form of biomolecules in living organisms is specifically determined by the electron spin state during their enzyme-catalyzed synthesis processes. Specifically speaking, the electrons released from the coenzyme NAD(P)H of amino acid synthase are heterogeneous in spin states; however, when they pass through the chiral alpha-helix structure of the enzymes to the site of amino acid synthesis at the other end of the helix, their spin states are filtered and polarized, producing only spin up electrons; once the spin-polarized electrons participate in the reductive reaction between alpha-oxo acid and ammonia, only L-amino acids are formed according to the Pauli exclusion principle.

Motivation & Objective

• To explain the origin of biological homochirality, specifically why life uses only L-amino acids.
• To address the long-standing puzzle of how a single chiral form emerged in biological systems despite racemic precursors.
• To propose a mechanism involving electron spin dynamics in enzymatic reactions as the driving force for chiral selection.
• To integrate quantum spin effects with biochemical processes in amino acid synthesis.

Proposed method

• Proposes that electrons from NAD(P)H are initially spin-heterogeneous during enzymatic reactions.
• Suggests that chiral alpha-helices in amino acid synthase act as spin filters, polarizing electrons to spin-up state.
• Applies the Pauli exclusion principle to explain why only L-amino acids are formed when spin-polarized electrons participate in reductive amination.
• Models the electron transfer process through chiral protein structures as a key step in chiral selection.
• Uses quantum mechanical principles to link electron spin state to stereochemical outcome in biochemical reactions.
• Analyzes the enzymatic reaction pathway involving alpha-oxo acids and ammonia, emphasizing spin-dependent electron transfer.

Experimental results

Research questions

• RQ1 How could a single chiral form of biomolecules emerge from a racemic prebiotic environment?
• RQ2 What physical mechanism could enforce enantioselective synthesis of L-amino acids in enzymatic systems?
• RQ3 Can electron spin polarization in chiral protein structures lead to selective formation of one enantiomer?
• RQ4 How does the Pauli exclusion principle influence stereochemistry in biochemical electron transfer?
• RQ5 What role do NAD(P)H-derived electrons play in establishing biological homochirality?

Key findings

• Electrons from NAD(P)H are initially spin-heterogeneous but become spin-polarized (spin-up) during transit through chiral alpha-helices in enzymes.
• The chiral environment of the enzyme's alpha-helix acts as a spin filter, selectively transmitting spin-up electrons.
• Spin-polarized electrons participate in reductive amination of alpha-oxo acids, leading to exclusive formation of L-amino acids.
• The Pauli exclusion principle is invoked to explain why only one enantiomer (L-form) is formed when spin-polarized electrons are involved.
• The mechanism provides a physical basis for the emergence of homochirality without requiring external chiral fields or symmetry breaking.
• The model is consistent with observed enzymatic pathways and offers a testable hypothesis linking quantum spin to biological stereochemistry.