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 SPTLC1, either SPTLC2 or SPTLC3, and either SPTSSA or SPTSSB. The composition of the complex will define the substrate specificity. Expressed in astrocytes. Expression in increased by palmitate at protein level but not mRNA level (PubMed:21994399). Expression is down-regulated by microRNA miR-9, miR29a and miR-29b-1 (at protein level) (PubMed:21994399). Belongs to the class-II pyridoxal-phosphate-dependent aminotransferase family.