Component of the serine palmitoyltransferase (SPT) that catalyzes the first committed step in sphingolipid biosynthesis, which is the condensation of an acyl-CoA species and L-serine. The catalytic core is composed of a heterodimer of sptl-1 and sptl-2 or sptl-1 and sptl-3 (By similarity). Required for the specification of abicobasal polarity and development of the gut lumen. H(+) + hexadecanoyl-CoA + L-serine = 3-oxosphinganine + CO2 + CoA Lipid metabolism; sphingolipid metabolism. Heterodimer of sptl-1/sptl-2 or sptl-1/sptl-3. Belongs to the class-II pyridoxal-phosphate-dependent aminotransferase family.