LEAD TOXICITY AND THE ALA-DEHYDRATASE POLYMORPHISM

delta -氨基乙酰丙酸脱水酶（ALA-D, EC 4.2.1.4）是一种锌

Delta-aminolevulinic acid dehydratase (ALA-D, EC 4.2.1.4) is a zinc metalloenzyme whose inhibition by lead is the first and most sensitive indicator of lead exposure and whose decreased activity has been clearly implicated in the pathogenesis of lead poisoning. The enzyme is encoded by two alleles, ALA-D1 and ALA-D2. Recent evidence from our laboratory indicates that individuals heterozygous or homozygous for the less common allele, ALA-D2, have blood lead levels 10 mu g/ml greater than similarly exposed individuals homozygous for the ALA-D1 allele who have blood lead levels in the range of 20-50 mu g/dl. These results suggest that there are genetically susceptible individuals who would be at an increased health risk if the fetuses of women with such a genetic susceptibility may be at higher risk for congenital anomalies. The biochemical basis for the differential genetic susceptibility of individuals carrying different isozymes of ALA-D is unknown. A molecular approach will be taken to facilitate studies of the ALA-D polymorphism and its association with blood lead levels. Using a full-length cDNA for human ALA-D as a probe, cDNAs for ALA- D1 and ALA-D2 will be cloned and sequenced to determine the precise nature of the polymorphism. ALA-D1 and ALA-D2-specific oligodeoxyribonucleotide probes will be used to confirm the common identity of the polymorphism in ALA-D 1-1 and 2-2 individuals. Alternatively the interaction of the ALA-D isozymes with lead, large quantities of human ALA-D 1-1 and 2-2 will be expressed in an purified from E. coli, and their physicokinetic properties will be compared with affinity purified isozymes from erythrocytes. All of these efforts will be directed toward elucidation of the biochemical basis for the differential genetic susceptibility to blood lead accumulation in individuals carrying different isozymes of ALA-D. In addition, a sensitive and rapid test will be developed to distinguish ALA-D 1 and 2 subunits using monoclonal antibodies produced to synthetic peptides containing unique ALA-D 1 and 2 epitopes. Such a test would be valuable for additional epidemiological studies aimed at identifying genetically susceptible individuals who would be at an increased health risk if exposed to lead in the workplace or environment.