The hunt for a retinal-specific aldehyde dehydrogenase in sheep liver.

Abstract

During past 7 years, a number of retinal-specific aldehyde dehydrogenases have been identified in rat (RaIDH1, el Akawi and Napoli, 1994; Posch et al, 1992; RalDH2, Wang t al, 1996; RALDH-1, Bhat et al, 1995; Labreque et al, 1993; Labreque et al, 1995) mouse (RALDH-2; Zhao et al, 1996) tissues. In higher mammals such as horse, sheep and human, the major Class 1 aldehyde dehydrogenase (A1DH) is known to oxidise retinal, but it has not been clearly established whether this is the major A1DH that oxidises retinal or whether there is another retinal-specific enzyme as well. The Class 1 A1DH in higher mammals is not specific for retinal; it readily oxidises a wide range of other aldehydes (Klyosov, 1996). For human Class 1 A1DH, previous kinetic studies have yielded varying estimates of the Km for all-trans- retinal. Using a spectrophotometric method giving a single reaction progress curve, Yoshida et al (1992) reported a Km of 0. 06 M, and using a similar method Klyosov (1996) reported a Km of 1. 1 μM. This difference is significant in considering the possible importance of the Class 1 A1DH in retinal metabolism in vivo, since cellular retinal concentrations are likely to be about 0. 1 μM (Yoshidaet al, 1992). The purpose of the current study was two-fold: firstly, to investigate the possibility that retinal-specific AlDHs are present in sheep as well as in rat and mouse sues, and secondly, to carry out more accurate kinetic characterisation of the Class AlDHs from sheep and human with retinal as a substrate.KeywordsAldehyde DehydrogenaseHuman ClassHigh MammalSheep LiverCellular Retinol Binding ProteinThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.