The light switch which activates enzymes

Together with his doctoral students Kim Steinborn (left) and Morten Peters Professor Rainer Herges (middle) has designed a ferrous molecule which properties can be changed via UV light. Photo/Copyright: private

Whether animals, plants, fungi, bacteria or people: enzymes containing iron are at work in almost all living organisms. In the human liver, such an enzyme acts like a kind of biological waste incinerator: it oxidises harmful substances, medication or the body's own materials, to excrete them via the kidneys.

In order to fulfil their vital task, the iron atom inside the enzyme constantly switches back and forth between a magnetic and non-magnetic state. An international research team led by Professor Rainer Herges from the Institute of Organic Chemistry at Kiel University (CAU) has now succeeded in designing for the first time an artificially-produced iron molecule, whose magnetic spin state can be switched on and off via UV light.

Spin is an intrinsic form of angular momentum – one of the primary characteristics of elementary particles – and a way to change the functions of molecules in a controlled manner. Such switches could also be used for numerous other applications, such as regulating further enzymatic reactions, chemical catalyses or for converting methane. The research team’s findings have been published recently in the renowned journal Nature Communications.

“Enzymes, such as the ferrous cytochrome P450 in our livers, operate as independent molecular machines,” explained Rainer Herges, Professor of Organic Chemistry and spokesperson for the Kiel Collaborative Research Centre 677 “Function by Switching”.

“Their biological functions are based on switching processes, which we explore and want to control as far as possible.” In collaboration with scientists from the Ruhr Universität Bochum (RUB), the Max Planck Institute for Chemical Energy Conversion (MPI CEC) and the National Institute for Interdisciplinary Science and Technology (NIIST) in India, they have now taken a further step towards achieving this: modelled on the cytochrome P450, they designed a ferrous molecule they can switch back and forth between different magnetic states using light in order to change their characteristics.

Molecular light switch activates enzymes

In the liver, the ferrous enzyme cytochrome P450 “lies in wait” for substrate molecules such as pollutants, in order to render them harmless. In this “standby” state, the enzyme is inactive and has a stable, so-called “low-spin”, i.e. many of its electrons are arranged in orderly pairs.

As soon as a pollutant molecule approaches and is detected by the ferrous enzyme, the molecule docks on the enzyme. The enzyme then changes to a “high-spin” state, in which most of the electrons are arranged individually (unpaired). In this state, the enzyme can also adsorb oxygen in addition to the pollutant molecule.

In a multi-stage process, the molecule is converted with the help of oxygen, and oxidises until it leaves the iron enzyme again in a harmless form. The enzyme then returns to the “low-spin” waiting position, and is ready to tackle the next pollutants.

“This change between the spin states in our molecule is triggered by a kind of 'light switch'. It activates the responsiveness of the enzyme,” explained Herges regarding the central mechanism, which the team can now control in the new molecule they created, by irradiation with light of different wavelengths. Targeted reactivity switching is crucial for the function of the enzyme.

“The reactions inside of the enzyme are very extreme. If the enzyme was permanently in reaction mode, it would destroy itself.”

Controlled methane conversion by bacteria

As a possible application for switchable iron enzymes the researchers consider the conversion of methane to methanol to produce liquid fuel. “When extracting crude oil, unused methane gas is released, which is deliberately burned by the oil drilling companies. As such, each year approximately 140 billion cubic meters of methane are destroyed, which we could convert into valuable fuel instead,” said Herges confidently.

This conversion is already possible by means of a technical process. However, it requires temperatures of over 400°C. In addition, more than half of the methane’s energy is lost. Bacteria, however, are able to convert methane into methanol at room temperature and with virtually no loss of energy.

To do so, it uses enzymes containing iron, so-called methane monooxygenases, whose spin states are also switchable. If the reactivity of the ferrous enzymes could be controlled in this way, then a biomimetic conversion of methane to methanol on a large scale is conceivable in future. Artificial molecules containing iron, such as those developed in the research group led by Rainer Herges, could then be used for efficient methanol production.

Photos are available to download:…
Caption: Together with his doctoral students Kim Steinborn (left) and Morten Peters Professor Rainer Herges (middle) has designed a ferrous molecule which properties can be changed via UV light.
Photo/Copyright: private…
Caption: In the so called „low-spin“ state the enzyme is not reactive. Only switched into the “high-spin“ state it is activated.
Foto/Copyright: Herges

Julia Siekmann
Science communication
Research focus Kiel Nano, Surface and Interface Science (KiNSIS)
Kiel University
Tel: 0431-880-4855

More information:

Details, which are only a millionth of a millimetre in size: this is what the priority research area “Kiel Nano, Surface and Interface Science – KiNSIS” at Kiel University has been working on. In the nano-cosmos, different laws prevail than in the macroscopic world – those of quantum physics. Through intensive, interdisciplinary cooperation between physics, chemistry, engineering and life sciences, the priority research area aims to understand the systems in this dimension and to implement the findings in an application-oriented manner. Molecular machines, innovative sensors, bionic materials, quantum computers, advanced therapies and much more could be the result. More information at

Kiel University (CAU)
Press, Communication and Marketing, Dr Boris Pawlowski, Text/editing: Julia Siekmann
Postal address: D-24098 Kiel, Germany, Telephone: +49 (0)431 880-2104, Fax: +49 (0)431 880-1355
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Prof. Dr Rainer Herges
Institute of Organic Chemistry
Kiel University
Tel.: +49 (0)431 880 2440

Light-controlled switching of the spin state of iron(III): Sreejith Shankar, Morten Peters, Kim Steinborn, Bahne Krahwinkel, Frank D. Sönnichsen, Dirk Grote, Wolfram Sander, Thomas Lohmiller, Olaf Rüdiger & Rainer Herges. Nature Communications Volume 9, Article number: 4750 (2018), DOI: 10.1038/s41467-018-07023-1…

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