So an Acyl group found on this chromogenic substrate. So this purple group basically attaches onto the oxygen. And so when that takes place, this blue section, the amide product is basically released and it's this amide product. So RNH two where the other H atom basically came from, this group here, this is the thing that produces that colored product. And so as this reaction takes place, the oscillation reaction takes place very, very quickly and that's why we have a fast initial birth stage. And as this is produced, this creates a color change and we can monitor that color change on the following graph.