CXCL12, also known as SCYB12, PBSF and SDF-1 beta, is an 8.3 kDa, heparin-binding member of the CXC (or alpha-) family of chemokines. SDF-1 is highly conserved between species, mouse CXCL12β shares approximately 92 % amino acid sequence identity with human CXCL12β. In all SDF-1 isoforms, SDF-1β is the canonical sequence. It has the complete amino acids in the C-terminal tail. On the cell surface, the receptor for this chemokine is CXCR4 and syndecan4. CXCL12 is strongly chemotactic for T-lymphocytes, monocytes, but not neutrophils. Although alpha and beta isoforms show similar activity, SDF-1 alpha is differentially processed, and different cells secrete the two isoforms. SDF-1 alpha and beta are reported to be monomers at neutral pH and physiologic ionic strength.

CXCL12 is belonging to the CXC chemokine family. SDF_x005f_x001e_1 alpha and SDF1 beta cDNAs encode precursor proteins of 89 and 93 amino acid residues, respectively. SDF-1 is highly conserved between species, mouse CXCL12α shares approximately 93% amino acid sequence identity with human CXCL12α. CXCL12 is strongly chemotactic for T-lymphocytes, monocytes, but not neutrophils. Contrast to SDF-1β, SDF-1α is shorter by four amino acids at the C-terminal tail.