Human liver fatty aldehyde dehydrogenase: microsomal localization, purification, and biochemical characterization.

To better understand the genetic disorder Sjogren-Larsson syndrome which is caused by a deficiency of fatty aldehyde dehydrogenase activity, we determined the subcellular localization of the enzyme and investigated its biochemical properties. Using density gradient centrifugation, we found that fatty aldehyde dehydrogenase activity was predominantly localized in the microsomal fraction in human liver. This fatty aldehyde dehydrogenase was solubilized from human liver microsomes and purified by chromatography on columns consisting of omega-aminohexyl-agarose and 5'-AMP-Sepharose 4B. The enzyme had an apparent subunit molecular weight of 54000, required NAD+ as cofactor, had optimal activity at pH 9.8, and was thermolabile at 47 degrees C. Fatty aldehyde dehydrogenase had high activity towards saturated and unsaturated aliphatic aldehydes ranging from 6 to 24 carbons in length, as well as dihydrophytal, a 20-carbon branched chain aldehyde. In contrast, acetaldehyde, propionaldehyde, crotonaldehyde, glutaraldehyde, benzaldehyde, and retinaldehyde were poor substrates. The enzyme was inhibited by disulfiram, iodoacetamide, alpha,p-dibromoacetophenone, and p-chloromercuribenzoate. These results indicate that microsomal fatty aldehyde dehydrogenase is a distinct human aldehyde dehydrogenase isozyme that acts on a variety of medium- and long-chain aliphatic substrates.

Chaperonin-mediated assembly of wild-type and mutant subunits of human propionyl-CoA carboxylase expressed in Escherichia coli.

We developed a bacterial expression system for the human alpha and beta cDNAs of propionyl-CoA carboxylase (PCC). These cDNAs (less the putative mitochondrial matrix targeting presequences) were co-expressed in Escherichia coli on one plasmid vector with each cDNA having its own IPTG-inducible promoter. Only negligible amounts of active PCC were measured despite the presence of both alpha and beta subunits as indicated by Western blot analysis and the almost complete biotinylation of the alpha subunit. Co-expression of this plasmid with a second plasmid vector over-expressing the E. coli chaperonin proteins, groES and groEL, resulted in a several hundred-fold increase in PCC specific activity, to a level comparable with that found in crude human liver extracts. PCC was partially purified on monomeric avidin affinity resin and the presence of both alpha and beta subunits was demonstrated, thereby confirming the assembly of both subunits into an active enzyme. Deficiency of either alpha PCC or beta PCC results in propionic acidemia, an autosomal recessive disorder. We used this expression system to characterize one missense mutation previously described in five Japanese alleles, namely C1283T (Thr428lle) in beta PCC. This mutation, when expressed in E.coli under the same conditions as that of wild-type PCC, had null activity, despite the presence of assembled alpha PCC and beta PCC subunits. This bacterial expression system can be useful for analysis of either alpha PCC or beta PCC mutations. Our findings indicated that the groES and groEL chaperonin proteins were essential for folding and assembly of the human PCC heteromeric subunits.

Prenatal diagnosis of Sjögren-Larsson syndrome using enzymatic methods.

Sjögren-Larsson syndrome (SLS) is an autosomal recessive disorder characterized by the presence of congenital ichthyosis, mental retardation, and spasticity. The primary biochemical defect in SLS has recently been identified to be a deficiency of fatty aldehyde dehydrogenase (FALDH), which is a component of fatty alcohol:NAD+ oxidoreductase (FAO). We monitored four pregnancies at risk for SLS by measuring FAO and FALDH in cultured amniocytes or cultured chorionic villus cells. The enzymatic results in one case using amniocytes obtained during the second trimester predicted an affected SLS fetus, which was confirmed at termination of the pregnancy. Another at-risk fetus was predicted to be affected with SLS using cultured chorionic villus cells obtained in the first trimester, and fetal skin fibroblasts confirmed a profound deficiency of FAO and FALDH. Two other fetuses were correctly predicted to be unaffected. These results demonstrate that SLS can be diagnosed prenatally using enzymatic methods.

Carrier detection for Sjögren-Larsson syndrome.

Sjögren-Larsson syndrome (SLS) is an autosomal recessive disorder associated with reduced activity of the fatty alcohol: NAD+ oxidoreductase complex (FAO). Recent studies indicate that SLS patients are specifically deficient in the fatty aldehyde dehydrogenase (FALDH) component of FAO. To investigate the possibility of carrier detection for SLS, FAO and FALDH activities were measured in cultured skin fibroblasts from normal controls, obligate SLS heterozygotes, and SLS homozygotes using the 18-carbon substrates octadecanol and octadecanal. Three of 11 heterozygotes for SLS had FAO activities that were within the normal range; the other 8 SLS heterozygotes had FAO activities below normal. In contrast, fibroblast FALDH activity was more effective than FAO in discriminating SLS heterozygotes from normal controls. FALDH activity (nmol min-1 (mg protein)-1) in normal controls was 8.54 +/- 1.16 (mean +/- SD; range 6.95-10.77; n = 12) and in SLS heterozygotes was 5.12 +/- 1.31 (range 3.28-6.96; n = 11), or 60 +/- 15% of mean normal activity. One SLS heterozygote had an FALDH activity within the lower range of normal; this heterozygote had an FAO activity below normal. None of the SLS heterozygotes had an FAO or FALDH activity that was in the range of that measured in SLS homozygotes. These results indicate that measurement of FAO and FALDH activities in cultured skin fibroblasts using 18-carbon substrates is useful for SLS carrier detection.

Cloning of the y1 Locus of Maize, a Gene Involved in the Biosynthesis of Carotenoids.

The y1 gene is one of the genes responsible for the production of [beta]-carotene in the endosperm and leaves of maize. We have cloned a Robertson's Mutator-tagged allele of the y1 gene (y1-mum) by using a Mu3 element as a hybridization probe. We substantiate that the cloned sequence is a portion of the y1 gene by molecular analyses of a revertant of a putative Mutator-induced y1 allele and the incidence of insertions within the cloned y1 sequence from several independently derived Mutator-induced y1 mutant stocks. The y1-mum sequence was used to isolate the standard Y1 allele, which conditions the presence of [beta]-carotene in the endosperm of the maize kernel.