Abstract
In our previously isolated human angiotensin preparation, the chemical structure has been completely elucidated and the β-carboxy group of aspartic acid residue was identified to be free but not amide, contrary to Boucher et al.'s speculation. Chemical unstability of asynthetic amide form angiotensin, however, still poses a question whether β-carboxy group might have been natively in amide form, and during the purification procedures employed, deamidated into a free form when analyzed at the finally isolated stage.
To solve this question, physico-chemical properties were compared between human angiotensin in various stages of purity and synthetic β-carboxy free and its amide form angiotensins. A synthetic amide form angiotensin was found partially approximately 15% deamidated resulting in two peaks through the same treatment as employed in the purification of human angiotensin. On the contrary, human angiotensin has never given such a two peakpattern in any chromatographies used. Synthetic amide form angiotensin migrated to the anode in paper electrophoresis at pH 8.4 regardless of the purity. Contrarily again, human angiotensin migrated to the anode only when it was contaminated with massive innert protein, and furthermore, this was found reversible.
All these results are in support that β-carboxy group of aspartic acid residue in human angiotensin is, not only in the finally isolated state but also natively, free.
