Formation of cobalt protoporphyrin in the liver of rats. A mechanism for the inhibition of liver haem biosynthesis by inorganic cobalt.

1. Treatment of rats with small doses of CoCl2 decreases liver 5-aminolaevulinate synthase (EC 2.3.1.37) activity and impairs incorporation of 5-amino[14C]laevulinate into liver haem. Salts of other metals (cadmium, nickel, manganese and zinc) are all relatively inactive. 2. The dose-response curves obtained for both these effects closely mirror the accumulation in the liver of a compound that is labelled by 5-amino[14C]laevulinate and is unextractable by acetone/HCl. 3. Incorporation of 5-amino[14C]laevulinate into unextractable compound is also obtained in vitro by incubating liver homogenates with label in the presence of cobalt:isotope-dilution experiments show that the radioactivity passes through pools of porphobilinogen and protoporphyrin, but not of haem. 4. The unextractable compound is not covalently bound to protein and possesses the same extraction and spectral properties as authentic cobalt protoporphyrin. 5. It is concluded (a) that cobalt protoporphyrin is readily formed not only in vitro, but also in vivo, and (b) that its formation accounts for the impaired incorporation of 5-aminolaevulinate into haem and may also be responsible for the action of cobalt on 5-aminolaevulinate synthase.     

The structure of cyanobacterial phycobilisomes: a model

Phycobilisomes, supramolecular complexes of water-soluble accessory pigments, serve as the major light-harvesting antennae in cyanobacteria and red algae. Regular arrays of these organelles are found on the surface of the thylakoid membranes of these organisms. In the present study, the hemi-discoidal phycobilisomes of several species of cyanobacteria were examined in thin sections of cells and by negative staining after isolation and fixation. Their fundamental structures were found to be the same. Isolated phycobilisomes possessed a triangular core assembled from three stacks of disc-shaped subunits. Each stack contained two discs which were 12 nm in diameter and 6–7 nm thick. Each of these discs was probably subdivided into halves 3–3.5 nm thick. Radiating from each of two sides of the triangular core were three rods 12 nm in diameter. Each rod consisted of stacks of 2 to 6 disc-shaped subunits 6 nm thick. These discs were subdivided into halves 3 nm thick.The average number of discs of 6 nm thickness forming the peripheral rods varied among the strains studied. For certain chromatically adapting strains, the average rod length was dependent upon the wavelength of light to which cells were exposed during growth. Analyses of phycobilisomes by spectroscopic techniques, polyacrylamide gel electrophoresis, and electron microscopy were compared. These analyses suggested that the triangular core was composed of allophycocyanin and that the peripheral rods contained phycocyanin and phycoerythrin (when present). A detailed model of the hemi-discoidal phycobilisome is proposed. This model can account for many aspects of phycobiliprotein assembly and energy transfer.Abbreviations PBS phycobilisome(s) - PBP phycobiliprotein(s) - AP allophycocyanin - PC phycocyanin - PE phycoerythrin - PEC phycoerythrocyanin - AP-B allophycocyanin B - C- cyanobacterial - R- rhodophytan - B- Bangiophycean - SDS sodium dodecyl sulfate - LPP Lyngbya-Plectonema-Phormidium group - Na-KPO₄ buffers NaH₂PO₄ titrated with a solution of KH₂PO₄ of equivalent molarity to a given pH     

Evolution des activités protéolytiques digestives chez les Jeunes Mulgilidae

Proteolytic activity in the stomach, pyloric caeca and intestine decreases with increasing size in the three fish species Mugil auratus, M. capito and M. saliens. Differences between these species are found mainly in the gastric proteolytic activity which appears to be related to diet. This activity is pronounced in M. saliens whose diet is mainly carnivorous. Comparison of regression lines relating gastric proteolytic activity to size reveals differences which distinguish M. auratus from both of the other species. Total proteolytic activity exhibits high variability depending on the types of diet.     

Thermo-inducible expression of cloned early genes of bacteriophage Mu.

An EcoRI fragment, containing approx. 5100 base pairs (bp) of the immunity-end of bacteriophage Mu, was inserted into the multicopy plasmid pMB9 by in vitro recombination. The expression of early Mu genes, located on the cloned fragment, is thermo-inducible because of the presence of the ts mutation in gene c. The isolation of a transformant harbouring the recombinant plasmid, pGP1, was possible only when expression of Mu genes was prevented. pGP1 can be maintained at 28 degrees C at high copy number, but at 42 degrees C the pGP1 containing cells are killed due to the expression of the kil gene of Mu. The following Mu genes are present on pGP1: the ner gene, the integration and replication genes A and B, the cim gene, and the kil gene. pGP1 containing cells do not show Gam and Sot activity at 42 degrees C, therefore the leftmost EcoRI site on the Mu DNA is located between genes kil and gam or sot, or within the gam or sot gene.     

The use of oral prostaglandin E2 in the management of intrauterine fetal death

12 otherwise healthy patients with intrauterine fetal death 1 to 6 weeks earlier were treated with oral prostaglandin E₂. 9 of the 12 patients delivered within 48 hours after treatment began. 2 others delivered within 48 hours after unsuccessful treatment ceased. In a third patient the cervix relaxed after treatment, and the uterine contents were removed by curettage. No serious complications, such as hemorrhage occurred. The uterus seemed surprisingly responsive to oral prostaglandin E₂ in cases of intrauterine fetal death.     

Influence of type of dietary fat on the prostaglandin release from isolated rabbit and rat hearts and from rat aortas

It has previously been found (1) that feeding rats a diet containing a high amount of sunflowerseed oil results in a higher coronary flow and left ventricular work of their isolated hearts as compared to hearts of rats fed hydrogenated coconut oil or lard. It was hypothesized that this phenomenon can be explained by an influence of dietary linoleic acid on prostaglandin synthesis in the heart. To verify this hypothesis rabbits and rats were fed for four weeks sunflowerseed oil (SSO), hydrogenated coconut oil (HCO) or lard (L) to a maximum of 30 to 40 per cent of the total digestable energy, and the prostaglandin release from the isolated perfused hearts and rat aortas was determined by gas chromatography and bio-assay (PGI₂).For the isolated hearts of rabbits fed SSO, the release of PGE₂, PGF_2α and 6-oxo-PGF_1α was 1.7, 0.7 and 3.0 ng min⁻¹ g⁻¹ dry weight respectively; when fed L, these values were 2.9, 1.1 and 5.6 ng min⁻¹ g⁻¹. For the isolated hearts of rats fed SSO, HCO or L, the total release of PGE₂, PGD₂, PGF_2α and thromboxane B₂ (TXB₂) was 5.9, 5.8 and 5.6 ng min⁻¹ g⁻¹ respectively; the release of 6-oxo-PGF_1α was 3.4, 5.7 and 6.4 ng min⁻¹ g⁻¹ respectively. Relatively, 26% PGE₂, 13% PGD₂, 8% PGF_2α, 6% TXB₂ and 47% 6-oxo-PGF_1α were released. For the isolated aortas of rats fed SSO or HCO, the release of PGI₂-like activity was 0.37 ± 0.05 and 0.49 ± 0.05 ng min⁻¹ cm⁻². The release of PGI₂-like activity from hearts of EFA-deficient rats was about 20% of that from control hearts.We conclude that, although feeding sunflowerseed oil, with respect to feeding hydrogenated coconut oil or lard, does increase coronary flow and left ventricular work, it does not increase the basal prostaglandin production in the isolated rat or rabbit heart; instead there is a tendency for a lower PGI₂ synthesis.