Eva A. Wider

Effect of cadmium, lead and arsenic on the oviposition, hatching and embryonic survival of Biomphalaria glabrata.

Biomphalaria glabrata is a widespread freshwater gastropod mollusc. The easy aquaculture of these organisms allow its use as an accessible tool for contamination bioassays. B. glabrata showed marked metabolic responses when exposed to cadmium, lead and arsenic. Those responses could also affect the reproduction of the snails. Taking into account this hypothesis, B. glabrata were exposed for 96 h (acute laboratory bioassays) to different concentrations of cadmium (0.1, 0.05 and 0 mg/L), lead (0.5, 0.1, 0.05 and 0 mg/L) and arsenic (0.5, 0.1, 0.05 and 0 mg/L). Snails were removed from the aquaria while eggs were left in the same contaminant concentrations. The effect of the assayed toxicants on snail reproduction was registered as the alterations of the total number of laid eggs (TNLE), hatching time and embryonic survival. At 0.10 mg/L cadmium significantly decreased the TNLE (p<0.05) and no embryos survived. The lowest assayed level (0.05 mg/L) of cadmium, delayed the hatching time twice when it was compared with the control group (p<0.01). Lead decreased the TNLE at 0.5 mg/L level (p<0.01). The other assayed doses (0.05 and 0.10 mg/L) also decreased embryonic survival significantly (p<0.05 and p<0.01 respectively) and extended twice the time to hatching (p<0.01). The 0.50 mg/L level killed all embryos. Arsenic at all studied concentrations decreased the TNLE (p<0.05) while the hatching time was increased by 50%. Embryo survival only decreased at the highest level (0.5 mg/L) of arsenic assayed. In summary, the acute exposure (96 h) to cadmium lead and arsenic, altered the reproduction of B. glabrata, modifying the TNLE, hatching time and embryonic survival.

Properties and regulatory effect on tetrapyrrole biosynthesis of succinyl CoA synthetase isolated from soybean callus tissue system.

Succinyl-CoA is involved in the early steps of the biosynthesis of tetrapyrrole compounds such a haem and chlorophyll and its formation is catalysed by sucnicyl-CoA synthetase (succinate: CoA ligase (GDP or ADP) EC 6.2.1.4 or 6.2.1.5). It has been purified from mammalian, bacterial and plant tissues such as spinach [I] , wheat leaves [2] , artichoke mitochondria [3] and tobacco [4] . This communication reports some properties of succinylCoA synthetase isolated and partially purified from soybean callus, a highly dividing tissue, useful for detecting active systems as was described by Miller [5] . The inhibitory effect of protoporphyrin and haemin on the enzyme is briefly discussed in relation to its probable regulatory action on the tetrapyrrole biosynthetic pathway.

In inherited porphyrias, lead intoxication is a toxogenetic disorder

1. delta-Aminolevulinic acid dehydratase (ALA-D), blood lead and several enzymes and metabolites of the heme biosynthetic pathway were measured in a number of symptomatic porphyric patients, 22 with acute intermittent porphyria, three with hereditary hepatic coproporphyria, 10 with hereditary porphyria cutanea tarda, two with erythropoietic protoporphyria and two with congenital erythropoietic porphyria and in 84 lead intoxicated persons. 2. In the 39 individuals suffering from the inherited porphyrias and in 32 lead poisoned patients with a 30-50% reduced deaminase, blood lead content was not sufficiently increased (average 28 micrograms%) to account for the greatly decreased activity of ALA-D (average 36% of controls). 3. After a relatively trifling lead exposure they developed the signs of acute lead intoxication. 4. A second group of lead intoxicated patients showing low ALA-D activity and corresponding high concentration of lead in blood, exhibited no other physiologic deviation in the enzymes and metabolites of porphyrin biosynthesis. 5. Individuals with inherited porphyrias are ultrasensitive to low level lead exposure and that lead would also act as a triggering factor. In these patients, lead intoxication can be considered a toxogenetic disorder. 6. An inversely linear correlation between ALA-D activity and blood lead content was obtained for both groups of lead intoxicated patients, however, a different constant (k) for each was obtained, which we have taken as a measure of lead toxogeneticity: k = 10 +/- 1 for lead intoxicated individuals with otherwise normal heme metabolism and k = 5 +/- 0.5 for lead intoxicated symptomatic porphyric patients. 7. Determination of erythrocytic ALA-D, besides blood lead, will be a valuable indicator for preventive medical care for these patients, when they are expected to be exposed to lead either environmentally or in their professional life.

Porphyrin biosynthesis in Rhodopseudomonas palustris—XII. δ-aminolevulinate synthetase switch—off/on regulation☆

The high levels of delta-aminolevulinate synthetase (ALA-S) in Rhodopseudomonas palustris cells grown anaerobically in the light (Ph) decrease to those found in cells grown aerobically in the dark (A), when the former cultures were vigorously oxygenated; simultaneously bacteriochlorophyll (Bchl) synthesis abruptly halted leading to diminished steady-state specific Bchl content. When flushing oxygen was interrupted, enzymic activity increased, whether chloramphenicol was present or not in the medium; if the protein synthesis inhibitor was added when oxygenation started, ALA-S declined in the same fashion as in its absence, but thereafter reactivation of the enzyme was lower than before. Succinyl-CoA-synthetase and ALA-dehydratase activities were also measured under the conditions described, and no changes at all have been observed. The existence of different forms of ALA-S in R. palustris depending on growth conditions is postulated along with the formation of low molecular weight factors which can modulate ALA-S activity by binding to the enzyme; a widespread mechanism in the adaptation of micro-organisms to changes in environment. It is also proposed that this particular regulatory phenomenon, could be referred to as a switch off/on mechanism controlling ALA-S activity in R. palustris.

Porphyrin biosynthesis in RP. Palustris—X. Purification and some properties of rhodanese

Abstract 1. 1. Rhodanese from Rhodopseudomonas palustris has been isolated and purified 105-fold with a yield of 3.6 and a sp. act. of 297,900. 2. 2. A mol. wt of 16,500 d was obtained, indicating that the Rhodanese from this source is a monomer.

Porphyrin biosynthesis in Rhodopseudomonas palustris. XI: Extraction and characterization of δ-aminolevulinate synthetase

Abstract 1. 1. Although the levels of ALA-S in photosynthetic (Ph) are higher than in aerobic (A) cells, physical and kinetic properties are similar. Optimum reaction pH is 7.5; maximal product formation occurs at 37°C. 2. 2. The enzyme has an absolute requirement for glycine. The addition of cysteine (CySH), glutathione (GSH), cystine or 2-mercaptoethanol to the reaction mixture does not greatly modify activity, instead it diminishes in the presence of ALA, indicating that the ALA-feedback inhibits its own synthesis. 3. 3. The enzyme is not stable when stored at −15°C; however, activity remains constant for at least 18 hr when different preparations are kept at 0–4°C. 4. 4. Evidence of the existence of one or two low molecular weight compounds which stimulate or stabilize ALA-S activity was found by dialysis of crude extracts. 5. 5. K m values for glycine, succinyl-CoA and pyridoxal phosphate were 1.5 x 10 −2 M, 1 x 10 −5 M and 1 x 10 −6 M respectively. 6. 6. Molecular weight was estimated to be 61 65,000 and no indication of active higher molecular weight species or subunits was obtained. 7. 7. Activity of R. palustris ALA-S can be efficiently regulated within the cell by the formation of one or two low molecular weight factors, depending on growth conditions and also through the levels of both glycine and ALA.