Assays for porphyrins, delta-aminolevulinic-acid dehydratase, and porphyrinogen synthetase in microliter samples of whole blood: applications to metabolic defects involving the heme pathway

Three micromethods are described for the assay of enzymes or products of the heme biosynthetic pathway in blood. A fluorometric method for the assay of protoporphyrin may be applied to the rapid screening of children for chronic lead poisoning. A colorimetric assay for delta-aminolevulinic-acid dehydratase may be applied to the detection of acute and chronic lead poisoning. A fluorometric assay for porphyrin formation from prophobilinogen is also described.

-Aminolevulinic acid dehydrase activity in the blood of men working with lead alkyls

Millar, J. A., Thompson, G. G., Goldberg, A., Barry, P. S. I., and Lowe, E. H. (1972).Brit. J. industr. Med.,29, 317-320. δ-Aminolevulinic acid dehydrase activity in the blood of men working with lead alkyls. The activity of erythrocyte ALA¹-dehydrase is inhibited in vivo at blood lead (Pb²⁺) levels within the upper range of normal (20-40 μg/100 ml) and in vitro at lead concentrations greater than 10^-7 M. In view of the high sensitivity of the enzyme to Pb²⁺, the levels of enzyme activity in the blood of men occupationally exposed to lead alkyls, particularly tetraethyllead, were measured. It was found that the enzyme activity in an exposed group of men was significantly less (P<0·001) than in a control group, the respective mean values being 220 and 677 units of enzyme activity. Tetraethyllead is metabolized in the body via triethyllead and diethyllead ions. As the latter compound possesses properties similar to Pb²⁺, it was synthesized in the laboratory and its effect on ALA-dehydrase was studied. Diethyllead ion was found to inhibit ALA-dehydrase activity at concentrations greater than 5 x 10^-5 M, although the degree of inhibition was less than that obtained with Pb²⁺. These results suggest that exposure to tetraethyllead can cause a decrease in erythrocyte ALA-dehydrase activity.

Environmental lead pollution in an urban soft-water area

An investigation has been reported on the clinical and metabolic effects of lead acquired by soft domestic water from lead plumbing systems in 23 Glasgow households. The lead content of water from cold taps was up to 18 times the upper acceptable limit and was proportional to the amount of lead in the plumbing system. The blood lead of 71 inhabitants of these houses showed a significant positive correlation with water lead content. Delta-aminolaevulic acid dehydrase activity, an extremely sensitive indicator of lead exposure, showed a significant negative correlation with water-lead content. Atmospheric lead was within acceptable limits in all but one house and no significant correlation could be found with biochemical measurements. A small number of clinical abnormalities were found but could not be directly attributed to lead toxicity. The results of the study underline the possible danger to health of lead plumbing systems in soft-water regions.

Cystathionine synthase activity in human lymphocytes: induction by phytohemagglutinin

Uncultured human leukocytes contain no detectable cystathionine synthase activity. A method is described in which the addition of phytohemagglutinin (PHA) to short-term lymphocyte cultures results in a significant induction of enzymatic activity. This PHA-stimulated activity has characteristics that resemble those previously described for cystathionine synthase of normal liver and cultured fibroblasts. Lymphocyte cystathionine synthase activity is completely dependent on the presence of homocysteine and is absent or severely deficient in extracts from individuals with the syndrome of homocystinuria. This system for induction of cystathionine synthase in lymphocytes thus provides a simple in vitro technique for (a) diagnosing homocystinuria, (b) studying the mechanism of enzyme regulation and differentiation, and (c) examining the nutritional and hormonal control of cystathionine synthase activity both in normal subjects and homocystinuric patients.

Haem biosynthesis studied in patients with rheumatoid arthritis

In a study of the urinary excretion of haem precursors in patients with rheumatoid arthritis, iron-deficiency anaemia, and in healthy controls, certain differences were found. In iron-deficiency anaemia the excretion of both porphobilinogen and delta-aminolevulinic acid was increased, whereas in patients with rheumatoid arthritis only the porphobilinogen excretion was increased.A further study on the erythrocyte activity of delta-aminolevulinic acid dehydrase showed a higher activity in the erythrocytes from patients with rheumatoid arthritis compared with healthy controls.

Depression of delta-aminolaevulic acid dehydrase activity by ethanol in man and rat

1.β-Aminolaevulic acid (ALA) dehydrase activity has been measured in the blood of man and rats and in the tissues of rats intoxicated with ethanol.

2. ALA dehydrase activity was significantly depressed in the blood of man. This depression follows closely on the elevation of blood ethanol and returns to normal pari passu with the ethanol level.

3. In rats intoxicated with ethanol there is a significant depression of ALA dehydrase activity in blood, liver and kidney but not in heart or spleen.

4. A scheme is proposed whereby an increase in the intracellular redox potential by ethanol increases sulphydryl cofactor concentrations leading to an inhibition of enzyme activity.