title: Inventory of 'slow exchanging' hydrogen atoms in human proinsulin and its derivatives: observations on the mass spectrometric analysis of deuterio-proteins in D(2)O.
abstract: Secondary structure elements of human proinsulin and of its tryptic products were compared by H/D exchange, in a single-pot, using mass spectrometry. Human proinsulin containing an N-terminal methionine, M-proinsulin, was engineered and converted into a perdeuterio derivative, which using an optimized mass spectrometric protocol and manual calculations gave a mass of 9669.6 (+/-1) Da showing the replacement, with deuterium of 146.4 from a total of 149 exchangeable hydrogen atoms (83 from amides and 66 from side-chains). Tryptic digestion of the perdeuterio-M-proinsulin, followed by the transfer of the digest from a deuterio- into a protio-medium showed, at the earliest time of analysis, that of the 27 (+/-1) D atoms retained in M-proinsulin, 24 (+/-1) were found in the insulin nucleus, M-insulin-RR, and 4.2 (+/-1) in the C-peptide-KR. A temporal analysis of the fate of D atoms in these species showed that whereas the C-peptide-KR rapidly exchanged its deuterium, losing all by 6 h, the loss of D atoms from M-proinsulin and M-insulin-RR was gradual and in each case, 12 deuterium atoms survived exchange for 72 h. At all time intervals the loss of D atoms from M-proinsulin mirrored that from M-insulin-RR plus the C-peptide-KR, suggesting that the secondary-structure elements of M-proinsulin are largely conserved in its two component parts.
authors.affiliation: School of Biological Sciences, University of the Punjab, New Campus, Lahore, Pakistan. sobs@cyber.net.pk
authors.forename: Qurra-Tul-Ann Afza
authors.initials: QA
authors.lastname: Gardner
authors.forename: Hooria
authors.initials: H
authors.lastname: Younas
authors.forename: Naeem
authors.initials: N
authors.lastname: Rashid
authors.forename: J Neville
authors.initials: JN
authors.lastname: Wright
authors.forename: Muhammad
authors.initials: M
authors.lastname: Akhtar