Serine palmitoyltransferase (SPT). The heterodimer formed with LCB1/SPTLC1 constitutes the catalytic core. The composition of the serine palmitoyltransferase (SPT) complex determines the substrate preference. The SPTLC1-SPTLC2-SPTSSA complex shows a strong preference for C16-CoA substrate, while the SPTLC1-SPTLC2-SPTSSB complex displays a preference for C18-CoA substrate (By similarity). Plays an important role in de novo sphyngolipid biosynthesis which is crucial for adipogenesis (By similarity). H(+) + hexadecanoyl-CoA + L-serine = 3-oxosphinganine + CO2 + CoA H(+) + L-serine + octadecanoyl-CoA = 3-oxoeicosasphinganine + CO2 + CoA Lipid metabolism; sphingolipid metabolism. Heterodimer with SPTLC1. Component of the serine palmitoyltransferase (SPT) complex, composed of LCB1/SPTLC1, LCB2 (SPTLC2 or SPTLC3) and ssPT (SPTSSA or SPTSSB) (By similarity). Belongs to the class-II pyridoxal-phosphate-dependent aminotransferase family.