Catalyzes the phosphorylation of sphingosine to form sphingosine 1-phosphate (SPP), a lipid mediator with both intra- and extracellular functions. Also acts on sphinganine (By similarity). Required for neurotransmitter release from neuromuscular junctions. Acts by recruiting the synaptic vesicle priming protein unc-13 to synapses (PubMed:22588719, PubMed:23223309) (Probable). a sphingoid base + ATP = a sphingoid 1-phosphate + ADP + H(+) Lipid metabolism; sphingolipid metabolism. Recruitment to the presynaptic membrane may be regulated by endogenous acetylcholine, which activates a muscarinic signaling pathway acting through gar-3, egl-30 and unc-73. Muscarinic-mediated recruitment of sphk-1 to presynaptic terminals requires calcium influx and the calcium-binding protein calm-1. Primarily observed on the outer surface of mitochondria in body wall muscles. Expressed in the majority of cholinergic and GABAergic neurons, body wall muscle, excretory canal cells, intestine, and hypodermis.