Authentic soybean β-amylase preparation, purified to homogeneity as judged by SDS-PAGE by using an affinity purification step, was composed of four p
I-differing isoforms. By chromatofocusing, these isoforms were separated into three fractions, designated as fractions 1-3 in the order of elution. Fraction 1 contained two isoforms having the same molecular mass (55,989 Da), as measured by mass spectrometric analysis, with different p
Is, 5.32 (Isoform I) and 5.22 (Isoform II). Fraction 2 showed a single isoform having a molecular mass of 55,994 Da and having a p
I of 5.09. This component, named Isoform III, existed rather in excess in a mixture of the authentic enzyme isoforms. The remainder (fraction 3) also contained a single component (Isoform IV) which has a molecular mass of 56,310 Da with a p
I of 4.97. Chemical analyses indicated that the N-termini and the C-terminal tripeptides of four p
I-separated isoforms mentioned are similar to one another, and are blocked and are NH
2-Val-Asp-Gly-COOH, respectively. Moreover, enzymic properties involving specific activity and the value of
kcat/
Km for the above three fractions are almost the same, and also agreed completely with those of an unfractionated authentic β-amylase preparation.
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