Movements of D. discoideum vegetative amoebae responding to pteridine 
chemoattractants, folate acid and pterin, were recorded. A vector analysis of 
these images was performed to partition the speed and orientation components of 
these motility patterns. This study demonstrates that in addition to orientation 
(chemotaxis), stimulated speed (chemokinesis) is an important component of the 
directed migration of these amoebae. Furthermore, the primary difference in 
their response to folate versus pterin is in speed rather than orientation. The 
data support a model of directed migration of these cells in which there are (1) 
separate signal translation pathways consequent from folate versus pterin 
reception and (2) specific pathways leading to increase in orientation versus 
speed.