Recombinant barley alpha-amylase 1 isozyme was constitutively secreted by Saccharomyces cerevisiae. The enzyme was purified to homogeneity by ultrafiltration and affinity chromatography. The protein had a correct N-terminal sequence of His-Gln-Val-Leu-Phe-Gln-Gly-Phe-Asn-Trp, indicating that the signal peptide was efficiently processed. The purified alpha-amylase had an enzyme activity of 1.9 mmol maltose/mg protein/min, equivalent to that observed for the native seed enzyme. The kcat/Km was 2.7 x 10(2) mM(-1) x s(-1), consistent with those of alpha-amylases from plants and other sources.