Stephen Halford was a biochemist whose innovative studies transformed our understanding of how enzymes interact with their substrates. He used relaxation spectroscopy to relate the dynamics of proteins in solution — similar to their natural state in the body — with their structure as revealed by X-ray crystallography.

Stephen’s studies of the type II restriction enzyme EcoRV, which cuts DNA and opens the way for genetic recombination in bacteria, showed that it ‘hops’ from one binding site to another, rather than ‘sliding’ as previously thought. He also revealed that although EcoRV can bind to any location on the DNA molecule, it only cuts at one specific site. Another such enzyme, SfiI, cuts DNA at two sites simultaneously, with the DNA sequence between forming a ‘loop’.

Through his use of quantitative biophysical methods, Stephen has solved problems previously inaccessible to the qualitative methods of molecular biology. He received the Novartis Prize and Medal of the Biochemical Society in 2001.

Professor Stephen Halford FRS died on 13 July 2022.