11-HYDROXYTHROMBOXANE B-2 DEHYDROGENASE IS IDENTICAL TO CYTOSOLIC ALDEHYDE DEHYDROGENASE

11-Hydroxythromboxane B-2 dehydrogenase purified from porcine kidney h as been identified as cytosolic aldehyde dehydrogenase (EC 1.2.1.3). T his identification is based on protein characteristics, sequence analy sis of one proteolytic digest, blocked N-terminus, subunit molecular m ass of 55 kDa, and enzymatic activities. The sequence difference with the human enzyme is 7.5% in the fragments analyzed (29 exchanges of 38 8 positions, corresponding to the expected species variability for cyt osolic aldehyde dehydrogenase). The substrate thromboxane B-2 contains a hemiacetal in its ring structure, but the reaction most likely proc eeds via the aldehyde form of the substrate. This finding is in agreem ent with the proposed metabolism of 4-hydroxycyclophosphamide and high lights the possibility that molecules containing a hemiacetal structur e can function as substrates for aldehyde dehydrogenase.