ɐ nˈʌmbɚɹ ʌv pɹˈoʊtiːnz hæv hɪstˈɔːɹɪkli bˌɪn pɹəpˈoʊzd tə fəsˈɪlᵻtˌeɪt ðɪs tɹˈænsfɜːɹ ɪŋklˈuːdɪŋ: stˈɛɹɑːl kˈæɹiɚ pɹˈoʊtiːn tˈuː ˌɛssˌiːpˈiː tˈuː, stˌɛɹɔɪdoʊdʒˈɛnɪk ˈæktᵻvˌeɪɾɚ pˌɑːlɪpˈɛptaɪd ˌɛsˌeɪpˈiː, pɚɹˈɪfɚɹəl bˈɛnzoʊdˌɪeɪzpˌaɪn ɹᵻsˈɛptɚ pˌiːbˌiːˈɑːɹ ɔːɹ tɹænsloʊkˈeɪɾɚ pɹˈoʊtiːn, tˈiːspˈoʊ, ænd sənt ˌeɪˈɑːɹ.
A number of proteins have historically been proposed to facilitate this transfer including: sterol carrier protein 2 (SCP2), steroidogenic activator polypeptide (SAP), peripheral benzodiazepine receptor (PBR or translocator protein, TSPO), and StAR.