The vesicle is actively transported down the axon along microtubules, seen in yellow, getting passed from one kinesin protein to the next. Meanwhile, inside the vesicle, enzymes called proteases, which were packaged into the vesicle with the propeptide, cleave the longer propeptide chain into several smaller pieces. These small chains, shown here in dark green, are the active neurotransmitters. The extra yellow pieces are inactive.