Abstract
Membrane-associated enzymes have been found to behave differently qualitatively and quantitatively in terms of activity. These findings were highly debated in the 1970s and many general correlations and reaction specific models have been proposed, reviewed, and discarded. However, new biological applications brought up the need for clarification and elucidation. To address literature shortcomings, we chose the intrinsically water-soluble enzyme a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) and large unilamellar vesicles with a relative broad phase transition. We here present activity measurements of ADAMTS13 in the freely dissolved state and the membrane associated state for phosphocholine lipids with different acyl-chain lengths (13:0, 14:0 and 15:0) and thus main phase transition temperatures. While the freely dissolved enzyme shows a simple Arrhenius behavior, the activity of membrane associated ADAMTS13 in addition shows a peak. This peak temperature correlates with the main phase transition temperature of the used lipids. These findings support an alternative theory of catalysis. This theory predicts a correlation of the membrane associated activity and the heat capacity, as both are susceptibilities of the same surface Gibb’s free energy, since the enzyme is attached to the membrane.
Highlights
Membrane-associated enzymes have been found to behave differently qualitatively and quantitatively in terms of activity
The authors state that the theory should be about the general field of catalysis
The main phase transition temperature is in accordance with literature[49]
Summary
Membrane-associated enzymes have been found to behave differently qualitatively and quantitatively in terms of activity. While the freely dissolved enzyme shows a simple Arrhenius behavior, the activity of membrane associated ADAMTS13 in addition shows a peak This peak temperature correlates with the main phase transition temperature of the used lipids. When they slightly modified the systems components to test their conclusion, they found that the discontinuity was caused by a change in the catalytic mechanism, as reviewed by Sanderman[30] This assumption is supported by Kumamoto et al.[24], who conclude that “[a] theory that employs the phase change can adequately accommodate all the data for temperature [‘]breaks[’] in Arrhenius plots”[24]. They emphasize the need of universality of the theory to be applicable to different membranes and enzymes. The authors state that the theory should be about the general field of catalysis
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