About

Thorsten Ritz is a Professor of Physics & Astronomy at the University of California, Irvine. His research group, known as the Ritz group, is focused on physical biology with an interest in understanding the molecular design of life. Their work explores the possibility that principles of quantum computing are involved in the magnetic sense of animals and investigates the quantum biology of photosynthesis. He is based in Rowland Hall at UC Irvine, where he contributes to advancing knowledge at the intersection of quantum physics and biological systems.

Research topics

• Physics
• Chemistry
• Biology
• Photochemistry
• Chemical physics

Selected publications

• Characterizing the magnetoreception in cryptochrome using a synthetic two-component system

  2025-03-21

  article1st authorCorresponding

  A number of organisms are guided by their detection of the geomagnetic field. Cryptochrome is a photodetector that detects magnetic fields, a function known as magnetoreception. However, how cryptochrome transduces a signal to effect signal transduction is not understood. Here, we have constructed a minimal genetic circuit in E. coli to investigate signal transduction by cryptochrome. We have created a chimera of cryptochrome with the two-component system histidine kinase protein CpxA. We have measured output of the chimera using a highly sensitive circuit consisting of a non-cognate response regulator and a transcriptional fluorescent protein reporter. Measurement under stimulation by a magnetic field and light suggest that the chimera is active. These experiments establish a foundation for experiments to determine the biophysical and biochemical mechanisms of magnetoreception.

  PublisherDOI

• Cryptochrome-dependent magnetoreception in a heteropteran insect continues even after 24 h in darkness

  Journal of Experimental Biology · 2021-09-06 · 24 citations

  articleOpen access

  Sensitivity to magnetic fields is dependent on the intensity and color of light in several animal species. The light-dependent magnetoreception working model points to cryptochrome (Cry) as a protein cooperating with its co-factor flavin, which possibly becomes magnetically susceptible upon excitation by light. The type of Cry involved and what pair of magnetosensitive radicals are responsible is still elusive. Therefore, we developed a conditioning assay for the firebug Pyrrhocoris apterus, an insect species that possesses only the mammalian cryptochrome (Cry II). Here, using the engineered Cry II null mutant, we show that: (i) vertebrate-like Cry II is an essential component of the magnetoreception response, and (ii) magnetic conditioning continues even after 25 h in darkness. The light-dependent and dark-persisting magnetoreception based on Cry II may inspire new perspectives in magnetoreception and cryptochrome research.

  PublisherOA PDFDOI

• Electron transfer and spin dynamics of the radical-pair in the cryptochrome from <i>Chlamydomonas reinhardtii</i> by computational analysis

  The Journal of Chemical Physics · 2020-02-10 · 15 citations

  articleSenior author

  In an effort to elucidate the origin of avian magnetoreception, it was postulated that a radical-pair formed in a cryptochrome upon light activation provided the basis for the mechanism that enables an inclination compass sensitive to the geomagnetic field. Photoreduction in this case involves formation of a flavin adenine dinucleotide (FAD)-tryptophan (TRP) radical-pair, following electron transfer within a conserved TRP triad in the cryptochrome. Recently, an animal-like cryptochrome from Chlamydomonas reinhardtii (CraCRY) was analyzed, demonstrating the role of a fourth aromatic residue, which serves as a terminal electron donor in the photoreduction pathway, resulting in the creation of a more distal radical-pair and exhibiting fast electron transfer. In this work, we investigated the electron transfer in CraCRY with a combination of free energy molecular dynamics (MD) simulations, frozen density functional theory, and QM/MM MD simulations, supporting the suggestion of a proton coupled electron transfer mechanism. Spin dynamics simulations discerned details on the dependence of the singlet yield on the direction of the external magnetic field for the [FAD•− TYRH•+] and [FAD•− TYR•] radical-pairs in CraCRY, in comparison with the previously modeled [FAD•− TRPH•+] radical-pair.

  PublisherDOI

• The reference-probe model for a robust and optimal radical-pair-based magnetic compass sensor

  The Journal of Chemical Physics · 2020-02-11 · 18 citations

  articleSenior authorCorresponding

  Radical-pair reactions have been suggested to be sensitive to the direction of weak magnetic fields, thereby providing a mechanism for the magnetic compass in animals. Discovering the general principles that make radical pairs particularly sensitive to the direction of weak magnetic fields will be essential for designing bioinspired compass sensors and for advancing our understanding of the spin physics behind directional effects. The reference-probe model is a conceptual model introduced as a guide to identify radical-pair parameters for optimal directional effects. Radical pairs with probe character have been extensively shown to enhance directional sensitivity to weak magnetic fields, but investigations on the role of the reference radical are lacking. Here, we evaluate whether a radical has reference character and then study its relevance for optimal directional effects. We investigate a simple radical-pair model with one axially anisotropic hyperfine interaction using both analytical and numerical calculations. Analytical calculations result in a general expression of the radical-pair reaction yield, which in turn provides useful insights into directional effects. We further investigate the relevance of the reference character to robustness against variations of earth-strength magnetic fields and find that the reference character captures robust features as well. Extending this study to radical pairs with more hyperfine interactions, we discuss the interplay between reference character and optimal and robust directional effects in such more complex radical pairs.

  PublisherDOI

• Quantum-Based magnetic sensing: How can birds detect 10 nT magnetic fields?

  Bulletin of the American Physical Society · 2020-03-03

  article1st authorCorresponding
  Publisher

• Arabidopsis cryptochrome is responsive to Radiofrequency (RF) electromagnetic fields

  Scientific Reports · 2020-07-09 · 31 citations

  articleOpen access

  How living systems respond to weak electromagnetic fields represents one of the major unsolved challenges in sensory biology. Recent evidence has implicated cryptochrome, an evolutionarily conserved flavoprotein receptor, in magnetic field responses of organisms ranging from plants to migratory birds. However, whether cryptochromes fulfill the criteria to function as biological magnetosensors remains to be established. Currently, theoretical predictions on the underlying mechanism of chemical magnetoreception have been supported by experimental observations that exposure to radiofrequency (RF) in the MHz range disrupt bird orientation and mammalian cellular respiration. Here we show that, in keeping with certain quantum physical hypotheses, a weak 7 MHz radiofrequency magnetic field significantly reduces the biological responsivity to blue light of the cryptochrome receptor cry1 in Arabidopsis seedlings. Using an in vivo phosphorylation assay that specifically detects activated cryptochrome, we demonstrate that RF exposure reduces conformational changes associated with biological activity. RF exposure furthermore alters cryptochrome-dependent plant growth responses and gene expression to a degree consistent with theoretical predictions. To our knowledge this represents the first demonstration of a biological receptor responding to RF exposure, providing important new implications for magnetosensing as well as possible future applications in biotechnology and medicine.

  PublisherOA PDFDOI

• The radical pair mechanism can provide a sensitive and robust magnetic compass for birds.

  Bulletin of the American Physical Society · 2020-03-06

  articleSenior author
  Publisher

• Cryptochrome mediated magnetic sensitivity in Arabidopsis occurs independently of light-induced electron transfer to the flavin

  Photochemical & Photobiological Sciences · 2020-02-17 · 58 citations

  article
  PublisherDOI

• Weak radiofrequency fields affect the insect circadian clock

  Journal of The Royal Society Interface · 2019-09-01 · 31 citations

  articleOpen access

  It is known that the circadian clock in Drosophila can be sensitive to static magnetic fields (MFs). Man-made radiofrequency (RF) electromagnetic fields have been shown to have effects on animal orientation responses at remarkably weak intensities in the nanotesla range. Here, we tested if weak broadband RF fields also affect the circadian rhythm of the German cockroach ( Blatella germanica ). We observed that static MFs slow down the cockroach clock rhythm under dim UV light, consistent with results on the Drosophila circadian clock. Remarkably, 300 times weaker RF fields likewise slowed down the cockroach clock in a near-zero static magnetic field. This demonstrates that the internal clock of organisms can be sensitive to weak RF fields, consequently opening the possibility of an influence of man-made RF fields on many clock-dependent events in living systems.

  PublisherOA PDFDOI

• Coupling <i>Drosophila melanogaster</i> Cryptochrome Light Activation and Oxidation of the Kvβ Subunit Hyperkinetic NADPH Cofactor

  The Journal of Physical Chemistry B · 2018-05-30 · 9 citations

  articleSenior author

  Motivated by the observations on the involvement of light-induced processes in the Drosophila melanogaster cryptochrome (DmCry) in regulation of the neuronal firing rate, which is achieved by a redox-state change of its voltage-dependent K+ channel Kvβ subunit hyperkinetic (Hk) reduced nicotinamide adenine dinucleotide phosphate (NADPH) cofactor, we propose in this work two hypothetical pathways that may potentially enable such coupling. In the first pathway, triggered by blue-light-induced formation of a radical pair [FAD•–TRP•+] in DmCry, the hole (TRP•+) may hop to Hk, for example, through a tryptophan chain and oxidize NADPH, possibly leading to inhibition of the N-terminus inactivation in the K+ channel. In a second possible pathway, DmCry’s FAD•– is reoxidized by molecular oxygen, producing H2O2, which then diffuses to Hk and oxidizes NADPH. In this work, by applying a combination of quantum and empirical-based methods for free-energy calculations, we find that the oxidation of NADPH by TRP•+ or H2O2 and the reoxidation of FAD•– by O2 are thermodynamically feasible. Our results may have an implication in identifying a magnetic sensing signal transduction pathway, specifically upon Drosophila’s Hk NADPH cofactor oxidation, with a subsequent inhibition of the K+ channel N-terminus inactivation gate, permitting K+ flux.

  PublisherDOI

Frequent coauthors

• Klaus Schulten

  30 shared

• Margaret Ahmad

  29 shared

• Maria Procopio

  Johns Hopkins University

  17 shared

• Klaus Brettel

  Institut de Biologie Intégrative de la Cellule

  13 shared

• Roswitha Wiltschko

  Goethe University Frankfurt

  13 shared

• Melih Şener

  Arizona State University

  12 shared

• Sanghyun Park

  Yonsei University

  12 shared

• Mohamed A. El‐Esawi

  12 shared