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 (PubMed:28698261). 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). Expressed in a variety of tissues. Expressed in brains cortices (at protein level) (PubMed:21994399). Expressed in brown and white adipose tissues (PubMed:28698261, PubMed:27818258). Expressed in liver (PubMed:27818258). In brains, expressed at low levels after birth, expression highly increases at 2 weeks after birth to decrease and be maintained at 4 weeks after birth until, at least, 18 months (PubMed:21994399). Expression increases in differentiated adipocytes (PubMed:28698261). Expression levels increase upon high-fat diet (at protein level). Adipocyte-specific knockout mice have reduced adipose tissue mass and develop hepatosteatosis with insulin resistance and hyperglycemia. Belongs to the class-II pyridoxal-phosphate-dependent aminotransferase family.