Conformation of aspergillopeptidase a in aqueous solution

The conformation of the extracellular acid proteinase of Aspergillus saitoi (aspergillopeptidase A, EC 3.4.4.17) has been investigated in aqueous solution. The optical rotation, $\text{[α]}{}_{\mathrm{<mtext>D</mtext>}}$, was −35°. The optical rotatory dispersion constant, $\text{λ}{}_{\mathrm{<mtext>c</mtext>}}$, was 207 mμ, and the Moffitt-Yang parameter, $\text{b}{}_0$, was zero. The $\text{−a}{}_0$ value in the Moffitt-Yang parameter or levorotation of the aspergillopeptidase. A molecule increased markedly in the presence of urea, while the value of $\text{b}{}_0$ remained unchanged. This finding indicates the absence of a helical conformation.

The infrared result indicates that the deuterium-exchanged aspergillopeptidase A exists in the antiparallel β structure. The location of an amide I band at 1632 cm⁻¹ has been observed. The spectrum has shown the presence of a weak band around 1685 cm⁻¹.

The location of the single tryptophan residue in aspergillopeptidase A is discussed.