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. 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. Widely expressed. Expression at protein level is highly increased in brains of patients with Alzheimer disease. No changes are observed at mRNA level. The disease is caused by variants affecting the gene represented in this entry. SPTLC2 disease mutations cause a shift in the substrate specificity of SPT resulting in the alternative use of L-alanine and L-glycine over its canonical substrate L-serine. This leads to the production of 1-deoxysphingolipids that cannot be correctly metabolized (PubMed:23658386). Belongs to the class-II pyridoxal-phosphate-dependent aminotransferase family. Extended N-terminus.