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. SPT complexes containing SPTLC3 generate shorter chain sphingoid bases compared to complexes containing SPTLC2. The SPTLC1-SPTLC3-SPTSSA isozyme uses C12-CoA, C14-CoA and C16-CoA as substrates, with a slight preference for C14-CoA. On the other hand, the SPTLC1-SPTLC3-SPTSSB has the ability to use a broader range of acyl-CoAs without apparent preference. H(+) + hexadecanoyl-CoA + L-serine = 3-oxosphinganine + CO2 + CoA dodecanoyl-CoA + H(+) + L-serine = 3-oxotetradecasphinganine + CO2 + CoA H(+) + L-serine + tetradecanoyl-CoA = 3-oxohexadecasphinganine + 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 white and brown adipose tissues. Belongs to the class-II pyridoxal-phosphate-dependent aminotransferase family.