Isolation and characterization of free haem from the shell gland of quail and hen

Free haem was isolated from the shell gland of the quail, Coturnix coturnix japonica, and of the fowl, Galinus domesticus, and characterized by HPLC-ESI-MS/MS. Quantification by HPLC gave values of 1.17-1.40 nmol/mg quail shell gland protein for haem, 1.66-2.17 nmol/mg protein for protoporphyrin and 0.25-0.40 nmol/mg protein for biliverdin. Possible implications of this previously unreported finding are discussed but they are not considered incompatible with the conclusion that all eggshell pigments are endogenously synthesized in the oviduct system.

Harderoporphyrin: a misnomer

More than 30 years ago it was reported that rodent Harderian glands contained a tricarboxylic acid porphyrin, which the authors named Harderoporphyrin. The recent finding in rat Harderian glands of the porphyrin glycoconjugate, protoporphyrin-1-O-acyl-beta-xyloside as a major component led to scrutiny of earlier publications. It became apparent that the results were flawed and that the conclusions were unsustainable. The procedural artefacts which led to the errors are discussed and their bases are demonstrated experimentally. Harderoporphyrin as originally defined never existed.

Porphyrins in urine, plasma, erythrocytes, bile and faeces in a case of congenital erythropoietic porphyria (Gunther's disease) treated with blood transfusion and iron chelation: lack of benefit from oral charcoal

Congenital erythropoietic porphyria is a rare genetic disorder in which deficiency of uroporphyrinogen III synthase results in excessive production of Type I porphyrins. The main clinical features are severe photodestruction of the skin and haemolytic anaemia. Treatment consists of shielding from light, blood transfusions and splenectomy, but is generally unsatisfactory. Previous studies have suggested that oral charcoal may be of benefit by binding porphyrins in the gut. A trial was therefore undertaken to evaluate this possibility. Porphyrins in urine, plasma and erythrocytes were measured by HPLC in a 23-year-old male patient with congenital erythropoietic porphyria, during an 8 week "run-in" period, and for a further 3 weeks when oral charcoal was given. Total urinary porphyrin excretion was 79-283 mumol/24 h consisting of 75% uroporphyrin I, 15% coproporphyrin I and smaller amounts of hepta-, hexa-, and pentacarboxylic porphyrins. Similar proportions were found in plasma and erythrocytes. During the first 24 h of charcoal administration a minor decrease in plasma and erythrocyte porphyrins was detected but this was not maintained during the remainder of the trial. In bile and faeces coproporphyrin I constituted approximately 95% of the porphyrins, with 2-3% coproporphyrin III and smaller amounts of pentaporphyrins I and III, but only trace amounts of uroporphyrin I. Oral charcoal was of no value in this case. Reasons are discussed in the context of biochemical differences between this patient with classical Gunther's disease and the similar clinical syndrome due to deficiency of uroporphyrinogen decarboxylase.

Drug treatment in acute porphyria

The acute hepatic porphyrias are rare pharmacogenetic diseases inherited as autosomal dominant conditions of low penetrance. The genetic defect is a 50% deficiency of an enzyme of the haem biosynthetic pathway. Patients may develop 'neurovisceral attacks' which include severe abdominal pain, neuropsychiatric manifestations and potentially fatal respiratory paralysis. Attacks occur generally after puberty, are much commoner in females and may be precipitated by endogenous hormonal changes, dieting, alcohol, severe infections, and many drugs. Treatment includes analgesia, early administration of haem, and general supportive measures. Patients are at greater risk of a severe attack on first presentation since an abdominal emergency may be simulated and inappropriate medication, including that for general anaesthesia may exacerbate the crisis. The urine should be tested for raised porphobilinogen, which is pathognomonic of the acute attack, if there is the slightest doubt about diagnosis. The genotype of blood relatives of index cases must be determined so that carriers may avoid drug and other precipitants. Some drugs have been established as safe or unsafe by clinical use, but information about many drugs is not available or is based only on their properties in rodents or in tissue culture systems. The relevance of these to the human condition remains controversial, but drugs shown to be porphyrinogenic in animal systems should be avoided if there is a known safe alternative. Where it is essential to use a drug not known to be safe, close biochemical and clinical observation may warn of an impending attack.

Mannose binding protein gene mutations associated with unusual and severe infections in adults

A defect in opsonisation can cause a common immunodeficiency. A mutation in mannose binding protein (MBP) caused by point mutations in the MBP gene will lead to such a defect. This type of syndrome can cause recurrent infections in infants between 6 and 18 months of age but is not generally believed to predispose to adult infections. We looked at 4 patients with severe and unusual infections in whom MBP gene mutations were the only identified cause of immunodeficiency and one patient with combined MBP and IgA deficiency. We analysed the MBP genotypes of all the patients in whom we suspected an immunodeficiency because of their clinical history. Infections seen were recurrent skin abscesses, chronic cryptosporidial diarrhoea, meningococcal meningitis with recurrent herpes simplex, and fatal klebsiella lobar pneumonia. Both sexes were affected and ages ranged from 15 to 56 years. Two patients were homozygous for codon 54 mutations, one patient had codon 52 and codon 54 mutations and was phenotypically homozygous, and two patients were heterozygous for codon 54 mutations. Individuals homozygous for MBP mutations are unusual in the general population (approximate frequency 0.3%). The occurrence of three homozygotes for MBP mutations among these five infected patients suggests that MBP deficiency may confer a life-long risk of infection.

Photosensitisation and photodynamic therapy of oesophageal, duodenal, and colorectal tumours using 5 aminolaevulinic acid induced protoporphyrin IX--a pilot study

The first study of photodynamic therapy in the human gastrointestinal tract using 5 aminolaevulinic acid (ALA) induced protoporphyrin IX as the photosensitising agent is described. Eighteen patients with colorectal, duodenal, and oesophageal tumours were studied. After 30-60 mg/kg of ALA given orally, biopsy specimens of tumour and adjacent normal mucosa were taken 1-72 hours later. These specimens were examined by quantitative fluorescence microscopy for assessment of sensitisation with protoporphyrin IX. Ten patients were given a second dose of ALA a few weeks later and their tumours were treated with red laser light (628 nm). With 30 mg/kg ALA, the highest fluorescence values were detected in the duodenum and oesophagus, and the lowest in the large bowel. Doubling the ALA dose in patients with colorectal tumours gave protoporphyrin IX fluorescence intensities similar to those in patients with upper gastrointestinal lesions and improved the tumour:normal mucosa protoporphyrin IX sensitisation ratio. The treated patients showed superficial mucosal necrosis in the areas exposed to laser light. Six patients had transient rises in serum aspartate aminotransferases, two mild skin photosensitivity reactions, and five mild nausea and vomiting. In conclusion, photodynamic therapy with systemically administered ALA may be a promising technique for the treatment of small tumours and areas of dysplasia such as in Barrett's oesophagus.

Uptake of protoporphyrin and continuous spectrophotometric assay for magnesium chelatase in Rhodobacter spheroides

Uptake of protoporphyrin was shown by Rhodobacter spheroides under anaerobic conditions in the dark. The process was not energy-dependent but required EGTA and was markedly stimulated by Methyl Viologen. Kinetic studies were consistent with a saturable process with Kd = 5-10 microM and Bmax. = 2.2 nmol of protoporphyrin bound/mg dry weight of cells. Bound protoporphyrin could be converted into magnesium protoporphyrin monomethyl ester under anaerobic conditions in the light or at low pO2 (6.3%) in the dark. This formed the basis of a sensitive continuous spectrophotometric assay for magnesium chelatase, which avoids the need to extract the product into organic solvent, and may facilitate the development of a cell-free system for magnesium chelatase in photosynthetic bacteria. It is proposed also that the uptake mechanism shown for exogenous protoporphyrin may indicate the existence of a ligand or carrier system for endogenously produced protoporphyrin essential for magnesium chelatase activity.

Sustained high plasma 5-aminolaevulinic acid concentration in a volunteer: no porphyric symptoms

The pathogenesis of the acute porphyric attack is not known. One hypothesis is that porphyrin precursors, especially 5-aminolaevulinic acid (ALA), are toxic for neuronal tissue. This was tested by infusing ALA in a male volunteer after a loading dose at a rate of 50-80 mg h-1 for 92.5 h. During the experiment plasma ALA concentration was 9-11 mumol 1-l and porphobilinogen concentration 3-6 mumol 1-l which are the levels seen during acute attacks. Urinary excretion of these porphyrin precursors was also markedly increased. ALA infusion caused no subjective symptoms and no change in pulse rate, blood pressure, or autonomic nerve function or conduction velocity of peripheral nerves. Photosensitivity was not demonstrable. It is concluded that sustained high plasma ALA concentration does not cause porphyria-like symptoms.

delta-Aminolaevulinic acid in plasma, cerebrospinal fluid, saliva and erythrocytes: studies in normal, uraemic and porphyric subjects

delta-Aminolaevulinic acid (ALA) was determined by g.l.c. with electron-capture detection. Normal plasma level was 92 nmol/l (SD = 39, n = 89, range 24-270 nmol/l). ALA was undetectable in 35 of 53 samples of normal cerebrospinal fluid (limit of assay 2 nmol/l). The mean of the other 18 samples was 19 nmol/l (SD = 10, range 6-36 nmol/l). Salivary ALA was generally only 10-30% of the plasma level in normal and porphyric subjects. Erythrocytes of normal and porphyric subjects contained no detectable ALA and were impermeable to its entry. ALA clearance correlated closely with that of creatinine, consistent with it being excreted by glomerular filtration with limited tubular reabsorption. In chronic renal failure, serum ALA was elevated to a maximum of three to four times the normal, but its urinary excretion was reduced, in keeping with lessened production. In two cases of acute intermittent porphyria with overwhelming neuropathy the maximum plasma levels of ALA were 9 and 12 mumol/l. Haematin infusion decreased the ALA levels but without obvious clinical benefit. Limited neurological recovery occurred without major reduction in plasma levels of ALA. One subject's attack was precipitated by pregnancy. The neonate was apparently normal, despite high levels of ALA in maternal plasma throughout gestation and a high level of ALA in the cord blood. The observations described here do not support the view that ALA may be directly neurotoxic.

Determination of delta-aminolaevulinic acid in biological fluids by gas-liquid chromatography with electron-capture detection

A derivative of delta-aminolaevulinic acid (AmLev), 2-methyl-3-acetyl-4-(3-propionic acid pentafluorobenzyl ester)pyrrole, with favourable properties for g.l.c. with electron-capture detection, was synthesized. Less than 1 pg could be detected on the column. 6-Amino-5-oxohexanoic acid formed the analogous derivative under similar conditions and was used as the internal standard in the development of a highly sensitive and specific assay for AmLev. The method has been applied to peripheral-venous and umbilical-cord plasma and to cerebrospinal fluid of normal and porphyric subjects.

Long term spironolactone and the adrenal cortex in essential hypertension

In view of recent evidence that spironolactone may inhibit synthesis of corticosteroids by a direct effect on the adrenal cortex, adrenocortical function was studied in eight patients with essential hypertension who had been treated with spironolactone from 3 months to 14 years. Their 24 h renal excretion of adrenocorticoid metabolites and the responses of cortisol, aldosterone and 18-hydroxy-11 -deoxycorticosterone (18-OH-DOC) to an incremental infusion of tetracosactrin (1-24 ACTH) were compared with those in eight patients with recently diagnosed essential hypertension who had received no spironolactone. The spironolactone-treated group had a significantly higher excretion of aldosterone, whilst the excretion of other adrenocorticoid metabolites did not differ. The same group also required less tetracosactrin to stimulate a detectable rise of plasma cortisol and 18-OH-DOC, they had greater plasma 18-OH-DOC responses at all infusion rates and, at the lowest infusion rates, had greater aldosterone responses. These results indicate that long-term spironolactone therapy does not inhibit adrenocortical function and may have some stimulatory effects.

Urine concentration of 3-ethyl-5-hydroxy-4,5-dimethyl-delta 3-pyrrolin-2-one ('mauve factor') is not causally related to schizophrenia or to acute intermittent porphyria

1. 3-Ethyl-5-hydroxy-4,5-dimethyl-delta 3-pyrrolin-2-one (HPL, 'mauve factor') was determined quantitatively in the urine of schizophrenic, general medical and porphyric subjects by a sensitive gas/liquid-chromatographic method using a nitrogen-specific detector. 2. A comparative evaluation with previously used methods for HPL was made and some problems of specificity are discussed. 3. The concentration of HPL in early morning and spot smaples of urine from 146 subjects with schizophrenia was not greater than that in 42 general medical patients, contrary to previous reports. 4. Of the three patients with acute intermittent porphyria, two excreted HPL. One subject, studied over a 2 year period, did so intermittently in a manner unrelated to her attacks of porphyria. 5. It is concluded that the urine content of HPL is unlikely to be causally related to schizophrenia or to the clinical manifestations of acute intermittent porphyria.

The 'mauve factor' of schizophrenia and porphyria, 5-hydroxyhaemopyrrole lactam, has low pharmacological potency on guinea-pig ileum

5-Hydroxyhaemopyrrole lactam, the 'mauve factor' reported in the urine of schizophrenics and porphyrics was found to inhibit electrically-stimulated contractions of guinea-pig ileum only at high concentrations (ID50 = 8.5 mM). This low potency makes it unlikely that the compound can account for neurotoxic effects in human porphyria.

Pharmacological properties of kryptopyrrole and its oxidation products on isolated sciatic nerve of rat and on guinea-pig ileum

1 Kryptopyrrole (2, 4-dimethyl, 3-ethylpyrrole) inhibited conduction in rat sciatic nerve by a local anaesthetic action. 2 Tone and both spontaneous and electrically-induced contractions of guinea-pig ileum were also inhibited by kryptopyrrole. The concentration of kryptopyrrole required for 50% inhibition of a maximum twitch tension (ID50) was 0.085 mM. 3 Oxidation products of kryptopyrrole with chromatographic properties similar to those of urinary constituents reported in schizophrenia and hepatic porphyrias had little or no effect at similar concentrations. 4 Dose-response curves to exogenous acetylcholine in guinea-pig ileum were shifted to the right by kryptopyrrole, with loss of parallelism and reduction in the maximum contraction. 5 Acetylcholine overflow from ileal segments at rest and during electrical stimulation was reduced by kryptopyrrole. 6 These results on ileal segments are consistent with kryptopyrrole having both a post-junctional site of action, presumably directly on the muscle, and a pre-junctional site reducing the output of acetylcholine from the myenteric plexus. 7 The significance of these findings is discussed in relation to a possible clinical pathological role for these compounds.

Control of magnesium-protoporphyrin chelatase activity in Rhodopseudomonas spheroides. Role of light, oxygen, and electron and energy transfer

1. Magnesium-protoporphyrin chelatase activity, previously shown in whole cells of Rhodopseudomonas spheroides, could not be demonstrated in cell-free extracts prepared in different ways, although spheroplasts retained moderate activity. Slight activity was detected also in whole cells of Rhodospirillum rubrum. 2. The effects on the activity of the enzyme of inhibitors of electron and energy transfer were studied in whole cells of Rps. spheroides. Amytal, rotenone, azide and cyanide inhibited at low pO(2) in the dark but not under anaerobic conditions in the light. Antimycin A and 2-heptyl-4-hydroxyquinoline N-oxide, as well as uncouplers and oligomycin, inhibited under all environmental conditions. 3. The effects on magnesium chelatase activity of intermediates of the tricarboxylic acid cycle, of thenoyltrifluoroacetone, of a number of artificial electron donors or acceptors, of various quinones and of the oxidation-reduction indicator dyes Benzyl Viologen and Methyl Viologen are described. 4. It was concluded that electron transport between a b-type and a c-type cytochrome as well as associated energy conservation and transformation reactions were essential for activity. There was also a specific requirement for ATP. 5. Exogenous protoporphyrin and magnesium protoporphyrin monomethyl ester were incorporated into bacteriochlorophyll or late precursors by whole cells. 6. Evidence is presented that the insertion of magnesium was the only step inhibited by oxygen in the biosynthetic pathway between protoporphyrin and bacteriochlorophyll.

Magnesium protoporphyrin chelatase activity in Rhodopseudomonas spheroides. Studies with whole cells

1. Whole cells of Rhodopseudomonas spheroides grown under semi-anaerobic conditions in the light incorporated magnesium into exogenous protoporphyrin when incubated with EDTA or the related chelators EGTA, N-(2-hydroxyethyl)-ethylenediamine-NN'N'- triacetate and trans-1,2-diaminocyclohexanetetra-acetate. 2. The reaction was demonstrated under anaerobic conditions in the light or at low oxygen partial pressure in the dark. Partial pressures of oxygen greater than 15% inhibited the reaction. 3. Cells grown under pure oxygen were completely inactive, but on adaptation to growth under low oxygen partial pressure (O(2)+N(2), 5:95) the development of activity paralleled the synthesis of bacteriochlorophyll. 4. The reaction with normal cells did not require protein synthesis, but cells that had lost their activity by being illuminated in Mg(2+)-deficient medium did not recover it in the absence of protein synthesis. 5. The product of the reaction was magnesium protoporphyrin monomethyl ester. 6. Evidence is presented that insertion of magnesium is obligatorily coupled with methylation and it is concluded that the reaction is dependent on a multienzyme complex.

Adaptation of Rhodopseudomonas spheroides

The composition of Rhodopseudomonas spheroides grown under oxygen or under air in the dark, or semi-anaerobically in the light was studied. The amounts of various constituents were expressed per cell. Anaerobically grown cells were 20 % lighter than cells grown under oxygen but contained approximately 50 % more protein and 85 % more phospholipid. The differences in weight were largely due to greater amounts of reserve material (poly-B-hydroxybutyrate and carbohydrate) in oxygen-grown cells. The major increase in the protein was due to a doubling of the 4particulate5 protein, the ‘soluble’ protein increasing by only 20% . The values of certain constituents in cells grown in air were intermediate between those of oxygen-grown cells and semi-anaerobically grown cells. The changes in composition were followed during adaptation from growth under oxygen to semi-anaerobic conditions in the light. Particulate protein, phospholipid, and enzymes concerned in bacteriochlorophyll synthesis increased markedly before photopigments or chromatophores were formed. These results indicate the sequence of some of the steps concerned in the differentiation of the cytoplasmic membrane of pigment-free microorganisms into the fully formed photosynthetic apparatus.

The isolation and characterization of subcellular fractions from pigmented and unpigmented cells of Rhodopseudomonas spheroides

Current ideas on the nature and development of the chromatophores of photosynthetic bacteria are reviewed. A simple method of obtaining purified chromatophores by sucrose density gradient centrifuging of cell-free extracts of Rhodopseudomonas spheroides is described. Such prepara­tions consist of about 60% protein, 20% phospholipid and 10% pigment, most of which is bacteriochlorophyll. Small quantities of carbohydrate, but only traces of nucleic acid, are found. The material was fairly homogeneous on electron microscopy. Rps. spheroides was also grown under pure oxygen in the dark. A particulate preparation from cells cultured under these conditions was similar to the chromatophores with respect to its high content of protein and of phospholipid but had a much greater content of nucleic acid and no bacteriochlorophyll. In addition, it contained amino sugars and diaminopimelic acid which are not found in chromatophores. These differences in chemical composition were correlated with the electron microscope appearances of the different subcellular fractions. It is concluded that the particulate preparation from cells grown under oxygen represents the cytoplasmic membrane of the micro-organism, but as isolated it is heavily contaminated with fragments of the cell wall from which it cannot be readily separated.

Distribution and metabolism of ornithine in Rhodopseudomonas spheroides

Ornithine lipid was found in chromatophores, in poorly pigmented subcellular fractions from pigmented micro-organisms and in fragments from cells grown under oxygen which have no bacteriochlorophyll. Its quantitative distribution among these different subcellular fractions did not correlate with the distribution of diaminopimelic acid. It is concluded that ornithine lipid is a specific constituent of the cytoplasmic membrane as opposed to the cell wall. Calculations indicate that about 20% of the ornithine lipid in pigmented cells is not associated with chromatophores. The cytoplasmic membrane content of unpigmented cells, calculated on the basis of ornithine lipid as a marker, was 15 to 22% of the total cell protein. Radioactivity from DL-[5- 14 C] ornithine in trace amounts was rapidly incorporated into growing cells. Most of the counts were in proline, arginine and glutamic acid residues of the proteins. However, nearly all the radioactivity incorporated into lipid was still present as ornithine. [5- 14 C]Ornithine incorporated into lipid of oxygen-grown cells did not turn over when the organisms were allowed to adapt to photosynthetic conditions but the lipid from the chromatophores was radioactive. During this adaptation the content of ornithine lipid per cell doubled with respect to the phospholipid, which increased twofold. The time course of these changes was parallel to that of bacteriochlorophyll synthesis. The significance of all these results in relation to the nature and biogenesis of the chromato­phores is discussed. It is pointed out also that studies on the distribution of ornithine lipid in other bacterial species may be of taxonomic importance.

The separation and identification of the lipids of Rhodopseudomonas spheroides

Detailed examination of the lipids of Rhodopseudomonas spheroides was undertaken since it was thought this might provide information on the biogenesis of the chromatophores. The phospholipids of purified chromatophores consist of phosphatidylethanolamine (35%), phosphatidylglycerol (34%) and phosphatidylcholine (23%); minor quantities of phosphatidic acid and of cardiolipin were also found. In addition, a sulpholipid was detected and also a new lipid containing ornithine. The relative proportions of the different phospholipids in chromatophores, in other subcellular fractions from pigmented micro-organisms and in fragments from cells grown under oxygen were similar. However, the ‘aerobic fragments’ contained much less ornithine lipid than the chromatophores. Comparison of the relative amounts of the different phospholipids in whole cells grown under oxygen, under air, or under semi-anaerobic conditions in the light showed no marked differences, the composition being similar to that found in chromatophores. It is concluded that there is no particular lipid specifically associated with chromatophores. Poly- β -hydroxybutyrate accounted for as much as 35% of the dry weight of cells grown under oxygen in the dark on malate-glutamate medium. It is necessary to remove this material before chromatography as it otherwise interferes with the separation.

Incorporation of radioactivity from [me-14C]methionine and [2-14C]glycine into the lipids of Rhodopseudomonas spheroides

Radioactivity from L-[Me- 14 C]methionine, in addition to being incorporated into pigments, as found by other workers, was incorporated into phosphatidylcholine, into phosphatidyl N -methylethanolamine and into phosphatidyl N, N -dimethylethanolamine. The latter two compounds were present in trace amounts only. Of the radioactivity in the phospholipid fraction, 90% was in the bases with only minor amounts in the fatty acids. Incorporation was also found into ornithine lipid. The presence of the pathway of phosphatidylcholine biosynthesis which proceeds by the successive methylation of phosphatidylethanolamine was shown by demonstrating a precursor-product relationship between the N -methylated phospholipids and phos­phatidylcholine. Evidence for the presence of the enzymes concerned in the biosynthesis of phosphatidyl­choline by the pathway mentioned and also for the incorporation of the methyl group into ornithine lipid has been obtained in cell-free systems from Rhodopseudomonas spheroides . The methyl donor was S-adenosylmethionine. Radioactivity from [2- 14 C]glycine was incorporated into ethanolamine, into choline and into fatty acids. Ethionine markedly reduced the incorporation into choline without affecting the labelling of ethanolamine. Thus it seems likely that the methyl carbons of choline were radioactive and that ethionine acted by inhibiting transmethylation from S-adenosylmethionine. It is concluded that the α -carbon of glycine gives rise to ‘one carbon’ fragments and also to acetate and the pathways by which these reactions occur are discussed.

Intracellular location of enzymes in rhodopseudomonas spheroides

By differential centrifugation of extracts of pigmented Rhodopseudomonas spheroides a number of constituents, phospholipid and lipid ornithine, and enzymes, zinc protoporphyrin chelatase, succinic dehydrogenase and S-adenosylmethionine-magnesium protoporphyrin methyltransferase, have been found to be associated both with chromatophores and with non-pigmented particulate material. These components are present in both types of material at about the same level. In extracts of non-pigmented organisms the particulate material contains some of the above components, but others are only present in low amounts. The subcellular structures present in the particulate material—ribosomes, cell wall and cytoplasmic membrane—have only been partially separated but, by comparing the distribution of the components listed above with those of known components of ribosomes and cell wall, it is probable that they are associated with cytoplasmic membrane. These studies suggest that the cytoplasmic membrane, apart from lacking the photosynthetic pigments, has a composition similar to that of chromatophores. The data are consistent with the conclusion drawn from electron microscopic studies that chromatophores are derived by invagination of the cytoplasmic membrane.

The relation between the pigment content of isolated chromatophores and that of the whole cell in Rhodopseudomonas spheroides

Conflicting reports in the literature on the relationship between the pigment content of chromatophores and that of the whole cells from which they have been isolated are reviewed. Chromatophores, isolated in sucrose density gradients from organisms grown at high light intensity or at very low oxygen tension in the dark, had a content of bacteriochlorophyll proportional to the pigment content of the cell. It was shown, however, by chemical analyses and by electron microscopy that these ‘chromatophores’ were heavily contaminated with other cellular structures. It is suggested that the inability to obtain pure material from cells grown under these environmental conditions is due to differences in their internal organization, resulting in a different pattern of fragmentation on disruption. When growth was at low to moderate light intensity, chromatophores of constant composi­tion were isolated from cells of different pigment content.

Metabolic turnover of the lipids of Rhodopseudomonas spheroides

Experiments with L-[Me- 14 C]methionine and inorganic 32 P indicate that the lipids of this micro-organism are metabolically stable. Lipids of unpigmented cells were incorporated into chromatophores when these cells were allowed to adapt to semi-anaerobic conditions in the light. The specific radioactivity of the phospholipid of the chromatophores was the same as that of the adapted cells; thus it appears that no distinction can be made between different parts of the cytoplasmic membrane system with respect to the labelling of the lipids. It is concluded that chromatophores originate from the cytoplasmic membrane and remain structurally a part of it.

The nature of the internal fine structure of Rhodopseudomonas spheroides as determined by the study of cell fragments

Treatment of Rhodopseudomonas spheroides with lysozyme and versene, followed by the application of mild shearing forces, has enabled the visualization by electron microscopy of the relationship of ehromatophores to the cytoplasmic membrane. Pigmented fragments were isolated also and on centrifuging in sucrose density gradients their properties were identical with those of chromatophores from cells disrupted by more vigorous methods. Since prolonged freezing of the cells or the presence of media of high ionic strength were required to obtain these results it is concluded that non-covalent bonding is of importance in holding the chromatophores to the rest of the cytoplasmic membrane.

The effect of adenosine triphosphate on porphyrin excretion and on glycine metabolism in Rhodopseudomonas spheroides

1. ATP, GTP, CTP and UTP at concentrations of 1mm markedly decrease the amount of coproporphyrin excreted by Rhodopseudomonas spheroides illuminated in a medium containing glycine, succinate and fumarate. 2. The effect of ATP is decreased if ethionine is also added to the medium. 3. Evidence is presented showing that ATP is taken up by the organisms from the medium. 4. ATP is shown to have a marked effect on the utilization of glycine. In the presence of ATP the incorporation of the methylene carbon atom of glycine into the fatty acid moieties of the phospholipids is greatly increased, and more of the carboxyl carbon atom is lost, probably as carbon dioxide. 5. ATP has little effect on the utilization of succinate or fumarate. 6. The possible significance of these results with regard to the control by ATP of porphyrin synthesis and excretion and glycine metabolism is discussed.