Abraham Atsmon

The heme biosynthetic pathway in lymphocytes of patients with malignant lymphoproliferative disorders

The metabolism of heme is impaired in lymphocytes of patients with malignant lymphoproliferative disorders (MLPO). Two of the enzymes of the heme biosynthetic pathway, delta-aminolevulinic acid dehydrase (ALAD) (EC 4.2.1.24) and ferrochelatase (FC) (EC 4.99.1.1) are markedly reduced. The activity of porphobilinogen deaminase (PBGD) (EC 4.3.1.8) is increased. The rate-limiting enzyme of heme biosynthesis in the liver, aminolevulinate synthase (ALAS) (EC 2.3.1.37) remains unchanged although the concentration of total heme in the lymphocytes is markedly reduced. This might reflect a lack of negative feedback inhibition by heme on ALAS activity in this system.

Activity of porphobilinogen deaminase in peripheral blood mononuclear cells of patients with metastatic cancer

Porphobilinogen deaminase (PBGD), one of the enzymes in the pathway of heme synthesis, was found to be elevated in peripheral mononuclear cells of 60% of patients with epithelial tumors and metastatic spread, but only in 14% of patients with tumor and no evidence of metastases. The combination of both high lactic dehydrogenase and high PBGD afforded a sensitivity of 40%, but a specificity of 96% in diagnosing metastatic spread.

Erythrocyte uroporphyrinogen synthase activity as a possible diagnostic aid in the diagnosis of lymphoproliferative diseases

Patients with active lymphoproliferative diseases were shown to have high activity of erythrocyte uroporphyrinogen synthetase (URO‐S), the enzyme which converts porphobilinogen to uroporphyrinogen. In a few patients examined the lymphocyte URO‐S was markedly increased. No correlation was found between the high URO‐S activity and the degree of anemia, reticulocytosis, or the presence of hemolysis. Patients with epithelial malignancies and with some common viral diseases had normal erythrocyte URO‐S values. Three patients with nonalcoholic cirrhosis also had high erythrocyte URO‐S activities. The determination of erythrocyte and lymphocyte URO‐S activity may be of aid in the diagnosis of lymphoproliferative diseases. It may also indicate whether remission has been achieved and whether treatment should be continued or reinstituted. These preliminary observations justify the investigation of a larger patient and control material.

The effects of succinylacetone (4,6-dioxoheptanoic acid) on δ-aminolevulinate synthase activity and the content of heme in monolayers of chick embryo liver cells

Succinylacetone was shown to inhibit aminolevulinate dehydratase (5-aminolevulinate hydro-lyase (adding 5-aminolevulinate and cyclizing), EC 4.2.1.24) to reduce cellular heme and porphyrins and to induce delta-aminolevulinate synthase (succinyl-CoA:glycine C-succinyltransferase (decarboxylating), EC 2.3.1.37) in monolayers of chick embryo liver cells. Marked synergistic effects on delta-aminolevulinate synthase activity were obtained by combining succinylacetone with levulinate and porphyrogenic drugs. The time course of delta-aminolevulinate synthase activity showed a delayed synergistic response.

The effect of DL-propranolol on γ-aminolevulinic acid synthetase activity and urinary excretion of porphyrins in allylisopropylacetamide-induced experimental porphyria

Abstract Experimental porphyria was induced in rats by allylisopropylacetamide. DL -Propranolol, a β-adrenergic-receptor blocking agent, significantly reduced the elevated urinary excretion of δ-aminolevulinic acid, porphobilinogen and total porphyrins. DL -Propranolol also partially prevented the increased activity of δ-aminolevulinic acid synthesis in liver homogenates of allylisopropylacetamide-treated rats. It had no effect on the above parameters in normal rats. These findings support the hypothesis that δ-aminolevulinic acid exists in two forms, a constitutive and an inducible one. In order to examine whether the action of the drug was caused by its membrane effect. D -propranolol and quinidine sulphate were used in similar sets of experiments. These drugs had no effect on the abnormal porphyrin metabolism of allylisoprpyl-acetamide-treated rats, indicating that the results obtained with DL -propranolol were not due to its membrane action.

The effect of agents blocking adrenergic β-receptors on incorporation of amino acids into protein in tissue cultures of chick embryo liver cells☆

Abstract The effect of β-receptor blocking agents on [14C] amino acid incorporation into protein in cultures of chick embryo liver cells was studied. DL-Propranolol, a β-blocker with non-specific membrane effects, caused a 40 per cent inhibition of incorporation of [14C] amino acids into protein. The inhibition was concentration dependent and reversible. A similar inhibition was obtained by oxprenolol (Trasicor), which is also a β-receptor blocking agent with non-specific membrane effects, and by the membrane active compounds: D-propranolol, lidocaine and quinidine. Pindolol (Visken), and practolol, which are almost devoid of membrane activity, were ineffective. These data indicate that the inhibitory effect of dl -propranolol and oxprenolol on protein synthesis is caused by their non-specific membrane effects.

The effects of metalloporphyrins, porphyrins and metals on the activity of delta-aminolevulinic acid synthase in monolayers of chick embryo liver cells

The effect of various metals, porphyrins and metalloporphyrins on the activity of delta-aminolevulinate synthase (ALAS) was measured in monolayers of chick embryo liver cells in order to determine whether the metal moiety of heme or heme itself is the regulator of ALAS activity. Iron, magnesium, zinc, copper, manganese and nickel did not decrease ALAS activity in non-induced and in cells induced by allyl-isopropylacetamide (AIA). Cobalt decreased both non-induced and induced activity. Porphyrins inhibited ALAS, apparently only after having been converted into metalloporphyrins. Almost all the metalloporphyrins examined decreased ALAS activity. None of the substances, at the concentrations used, was toxic to the cells. These observations indicate that probably heme and not iron is the regulator of ALAS activity in monolayers of chick embryo liver cells.

Inhibitory effect of membrane active compounds on induction of tyrosine aminotransferase in chick embryo liver cells in culture

In the course of investigations on the effect of beta-adrenergic receptor blocking agents in experimental porphyria we observed an inhibitory action of DL-propranolol and other membrane active compounds on the induced activity of delta-aminolevulinate synthetase Q-ALAS) (EC 3.2.1.37) both in vivo and in vitro [l-3] . Beta-adrenergic receptor blocking agents compete with catecholamines for activation of beta-adrenergic receptors. Some of these agents also possess non-specific membrane effects such as changes in depolarisation and/or repolarisation of the cellular membrane, local anesthetic and anti-arhythmic properties, etc. Other drugs, which have no betareceptor blocking effects, including quinidine and lydocain, have non-specific membrane activity and are regarded as membrane active compounds. The various membrane effects of these drugs and of betareceptor blockers are, at least partially, dissimilar. In order to determine whethertheinhibitory effect of DL-propanolol and other membrane active compounds is specific for induction of &-ALAS, we examined their effect on induction of another inducible enzyme, tyrosine aminotransferase (TAT) (EC 2.6.1 S). TAT is a soluble enzyme, the activity of which is increased by administration of steroid hormones with glucocorticoid activity, both in rat liver [4] and in hepatoma cells in culture [5,6]. Dexamethasone is known to be a potent inducer in cultured hepatoma cells. It raises TAT activity 4-8 fold in this system [7,8]. Our experiments were carried out in cultures of chick embryo liver cells.

Growth rate determines activity of porphobilinogen deaminase both in nonmalignant and malignant cell lines

PBGD activity and growth rate were determined in cultures of rat embryo fibroblasts, nontransformed and MLV/MS transformed fibroblastic cell lines; NIH-3T3 cells, and in a mouse lymphosarcoma cell line [L-929]. The two parameters examined correlate positively (P less than 0.001). The results of this investigation would seem to indicate clearly that porphobilinogen deaminase activity is related to growth. However, these experiments do not rule out the possibility that malignant transformation per se also causes changes in porphobilinogen deaminase activity.

A method for obtaining high recovery of purified subcellular fractions of rat liver homogenate

Abstract A method for obtaining highly purified subcellular fractions of rat liver is described. The recovery of each fraction approaches 100%. The method is based on differential centrifugation and the use of appropriate concentrations of Triton X-100 and MgCl 2 at certain specific steps in the fractionation procedure.