[6] These helical bundles contain important histidine residues that play a role in the pH regulation of dinoflagellate luciferase activity.
[6] Specifically, the presence of N-terminal intramolecularly conserved histidine residues are shown to be responsible for the loss of activity of the enzyme at high pH.
[6] At pH 8, the histidine residues remain unprotonated, interacting with a network of hydrogen bonds that block substrate access to the active site.
[6] Realistically, alanine replacement does not occur spontaneously; however, this experimental result provides further evidence that the larger histidine residues block access to the active site of the enzyme.
[10] Although the primary mechanism is unknown, voltage-gated ion channels on scintillon membranes open, allowing an influx of protons to enter the organelle lowering the pH sufficiently for dinoflagellate luciferase to activate.