We report evidence for the effect of very low magnetic fields on a biological reaction. The presence of magnetite particles (with permanent magnetic moment of 1 emu/g) in the assay had a 30-fold increase on the rate of reaction of horseradish peroxidase. The activity of this enzyme was evaluated with two chromogen systems, and the apparent Michaelis−Menten kinetic parameters were extracted.

Bio‐nanocatalysts (BNCs) consisting of horseradish peroxidase (HRP) self‐assembled with magnetic nanoparticles (MNPs) enhance enzymatic activity due to the faster turnover and lower inhibition of the enzyme. The size and magnetization of the MNPs affect the formation of the BNCs, and ultimately control the activity of the bound enzymes. Smaller MNPs form small clusters with a low affinity for the HRP. While the turnover for the bound fraction is drastically increased, there is no difference in the H2O2 inhibitory concentration. Larger MNPs with a higher magnetization aggregate in larger clusters and have a higher affinity for the enzyme and a lower substrate inhibition. All of the BNCs are more active than the free enzyme or the MNPs (BNCs > HRP ≫ MNPs). Since the BNCs show surprising resilience in various reaction conditions, they may pave the way towards new hybrid biocatalysts with increased activities and unique catalytic properties for magnetosensitive enzymatic reactions.