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Biomedical subjects

S Sassa

Publications and source records attributed to S Sassa.

At least 235 records · Page 13Linked to original sources
PubMed1975

Heme biosynthesis in bacterium-protozoon symbioses: enzymic defects in host hemoflagellates and complemental role of their intracellular symbiotes.

Heme biosynthetic activity in the symbiotic association involving crithidial flagellates and intracellular bacteroids was studied by enzymic, nutritional, and isotope incorporation experiments. Component organisms and their complexes in this association were analyzed separately to determine the underlying cause of the hemin requirement of hemoflagellates and the role of symbiotes in sparing this requirement of two crithidial species. Nutritional study of symbiote-free flagellates showed that their growth requires at least 0.1 mug/ml of hemin, which can be substituted by protoporphyrin IX, but not by the porphyrin precursors, delta-amino-levulinic acid or porphobilinogen. These flagellates, in the presence of protoporphyrin IX, incorporated 59Fe into heme, indicating that they possess ferrochelatase (EC 4.99.1.1), the terminal enzyme in the heme biosynthetic pathway, which catalyzes the insertion of iron into protoporphyrin IX. In symbiote-containing flagellates serially cultured in a defined medium free of tetrapyrrole compounds, heme and porphyrins can be detected by a fluorophotometric method, indicative of heme biosynthesis. Study of [14C]glycine incorporation into heme showed that the rate is much higher in symbiote-containing flagellates than in those without symbiotes. Microassay of uroporphyrinogen I synthase [EC 4.3.1.8; porphobilinogen ammonia-lyase (polymerizing)] revealed that the specific activity is high in symbiote-containing flagellates and higher still in isolated symbiotes, but essentially negligible in symbiote-free organisms. It is concluded that the bacterial symbiotes augment a very limited heme biosynthetic capacity of host flagellates by supplying uroporphyrinogen I synthase and perhaps other enzymes preceding ferrochelatase in the heme biosynthetic chain.

Aminolevulinic Acid↗
PubMed1974

A microassay for uroporphyrinogen I synthase, one of three abnormal enzyme activities in acute intermittent porphyria, and its application to the study of the genetics of this disease.

A new spectrofluorometric assay is described for quantitating uroporphyrinogen I synthase (EC 4.3.1.8) activity in volumes of human blood as small as 2 mul. By this sensitive assay the inheritance of the enzyme's activity has been studied and the genetic defect for acute intermittent porphyria has been confirmed to be autosomal dominant in nature. There is a 3-fold range of uroporphyrinogen I synthase activity in erythrocytes in the normal population, with a mean V(max) +/- SD of 35.7 +/- 8.4 nmol of uroporphyrinogen I formed per ml of erythrocytes per hr, at 37 degrees . One-half this level of enzyme activity (18.0 +/- 5.0) is found in erythrocytes from patients with clinically manifest acute intermittent porphyria; and in erythrocytes from those of their relatives, including prepubertal children, who have the latent gene defect for the disease. The K(m) of erythrocyte enzyme of normal people is 12.3 +/- 3.9 muM, whereas the K(m) of the erythrocyte enzyme of patients with acute intermittent porphyria is 6.2 +/- 3.9 muM, as determined on whole blood lysates. Three enzymic changes have now been identified in patients with acute intermittent porphyria; a high level of delta-aminolevulinate synthase activity; a low level of uroporphyrinogen I synthase activity; and a deficiency of steroid Delta(4)-5alpha reductase activity.

Adolescent↗
PubMed1974

Stimulators and inhibitors of hepatic porphyrin formation in human sera.

Human sera were found to contain factors that stimulate and factors that inhibit porphyrin formation by cultured avian liver cells. The capacity of sera to stimulate or inhibit porphyrin formation varied in different hormonal states and in the porphyrias. Sera from 31 post partum women, eight of whom were not lactating, inhibited porphyrin formation to a mean level 30% below the level in control cultures and also inhibited drug and steroid stimulation of porphyrin formation. In contrast, mean porphyrin formation compared to control cultures was increased between 9 and 21% by sera from 52 normal subjects, 16 women on oral contraceptives, and 11 pregnant women. It was increased 193% by sera from nine subjects with acute intermittent porphyria and 172% by sera from 13 subjects with porphyria cutanea tarda. Heated sera or ethanol extracts of sera from all groups of subjects further increased the mean porphyrin stimulation by sera and, for the post partum subjects, eliminated the inhibitory effect. Ethanol extracts of sera from 28 oral contraceptive-treated women caused significantly greater mean stimulation of porphyrin formation than did extracts of sera from 30 normal women. While sera from 17 out of 22 porphyric subjects contained both stimulatory and inhibitory factors, 5 out of 22 had no evidence of an inhibitory component. There appeared to be heterogeneity in the occurrence of the factors among porphyrics.The factor(s) in sera responsible for porphyrin stimulation were heat-stable and insensitive to trypsin; were present in the supernates after ethanol precipitation of plasma proteins; were extractable in ethyl acetate and nondialyzable; and they migrated with the albumincontaining fraction of serum during electrophoresis. The factor(s) responsible for porphyrin inhibition were heat labile, sensitive to trypsin, and resistant to neuraminidase; were present in the ethanol precipitates of sera and were nondialyzable; and they migrated with the gamma globulin fraction of serum during electrophoresis. Inhibition of porphyrin formation was not attributable to heme, free or bound as hemoglobin, hemopexin, or hemalbumin.

Adolescent↗
PubMed1972

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.

Acute Disease↗
PubMed1970

Induction of -aminolevulinic acid synthetase in chick embryo liver cells in cluture.

delta-Aminolevulinic acid synthetase is induced in chick embryo liver culture by the natural steroid, etiocholanolone, and by the foreign chemical, 3,5-dicarbethoxy-1,4-dihydrocollidine at the level of transcription. Alternatively, inducing chemicals such as allylisopropylacetamide and gamma-hexachloro-cyclohexane act primarily at the level of translation. Hemin (K(i) = 5 muM) inhibits the induction at the level of translation. In liver cell culture, the half-life of delta-aminolevulinic acid synthetase is 3 hr, that of mRNA about 5 hr.

5-Aminolevulinate Synthetase↗
PubMed1969

The occurrence of substances in human plasma capable of inducing the enzyme delta-aminolevulinate synthetase in liver cells.

We have demonstrated the presence, in the plasma of several patients with acute intermittent porphyria, of a substance which strongly induced the synthesis of porphyrins in chick embryo liver cells growing in primary culture. The induction response evoked by this humoral agent was in all respects similar to that elicited by drugs and hormones which are known to enhance porphyrin production by inducing the de novo formation of delta-aminolevulinate synthetase, the rate-limiting enzyme in this pathway. Inducing properties were not found in the plasma of normal individuals or in that from porphyric patients in remission. Significant inducing activity was, however, found in the plasma of some normal subjects ingesting drugs or contraceptive steroid mixtures. The occurrence of a potent inducer of delta-aminolevulinate synthetase in the plasma of certain porphyric patients may have clinical significance for these genetically susceptible individuals. It will also permit chemical characterization of those humoral agents which may be related to the episodic exacerbations of this hereditary liver disease.

Animals↗