The reduction of alpha-aminoadipate to alpha-aminoadipic delta-semialdehyde by a cell-free extract of Saccharomyces is shown to be a three-step process. First the amino acid reacts with ATP to form an adenylyl derivative. Then the adenylyl derivative of alpha-aminoadipate is reduced in the presence of NADPH. In the third step the reduced adenylyl derivative of the amino acid is cleaved to form alpha-aminoadipic delta-semialdehyde. The presence of Mg(2+) is necessary for the first and second steps. The third step does not need any cofactors. The product of the first step was isolated by chromatography after incubating the cell-free extract of Saccharomyces with alpha-aminoadipate, ATP and Mg(2+). The isolated product was identified as an adenylyl derivative of alpha-aminoadipate and could be converted into alpha-aminoadipic delta-semialdehyde under the stated experimental conditions. The product of the second step was too unstable to be identified.