11-Hydroxythromboxane B2 dehydrogenase is identical to cytosolic aldehyde dehydrogenase

11-Hydroxythromboxane B2 dehydrogenase purified from porcine kidney has been identified as cytosolic aldehyde dehydrogenase (EC 1.2.1.3). This identification is based on protein characteristics, sequence analysis of one proteolytic digest, blocked N-terminus, subunit molecular mass of 55 kDa, and enzymatic activities. The sequence difference with the human enzyme is 7.5% in the fragments analyzed (29 exchanges of 388 positions, corresponding to the expected species variability for cytosolic aldehyde dehydrogenase). The substrate thromboxane B2 contains a hemiacetal in its ring structure, but the reaction most likely proceeds via the aldehyde form of the substrate. This finding is in agreement with the proposed metabolism of 4-hydroxycyclophosphamide and highlights the possibility that molecules containing a hemiacetal structure can function as substrates for aldehyde dehydrogenase.