raku tsütoplasmas asuvad türosiinkinaaside perekonda kuuluvad ensüümid, mis seostuvad mõnede ensüüm-seotud raku pinna retseptorite tsütoplasmapoolse otsaga (nt T-rakkude antigeeni retseptor), millele endal puudub türosiinkinaasne aktiivsus, Src kinase family is a family of non-receptor tyrosine kinases that includes nine members: Src, Yes, Fyn, and Fgr, forming the SrcA subfamily, Lck, Hck, Blk, and Lyn in the SrcB subfamily, and Frk in its own subfamily. Frk has homologs in invertebrates such as flies and worms, and Src homologs exist in organisms as diverse as unicellular choanoflagellates, but the SrcA and SrcB subfamilies are specific to vertebrates.