Modulation of the oxygen affinity of cobalt-porphyrin by globin. (1/12)

We have combined two extreme effects which influence the oxygen affinity to obtain a cobalt-based oxygen carrier with an affinity similar to that of human adult hemoglobin (HbA). The goal was to obtain an oxygen transporter with a lower oxidation rate. Exchange of the heme group (Fe-protoporphyrin IX) in Hb with a cobalt-porphyrin leads to a reduction in oxygen affinity by over a factor of 10, an oxygen affinity too low for use as a blood substitute. At the other extreme, certain globin sequences are known to provide a very high oxygen affinity; for example, Hb Ascaris displays an oxygen affinity 1000 times higher than HbA. We demonstrate here that these opposing effects can be additive, yielding an oxygen affinity similar to that of HbA, but with oxygen binding to a cobalt atom. We have tested the effect of substitution of cobalt-porphyrin for heme in normal HbA, sperm whale (SW) Mb (Mb), and high affinity globins for leghemoglobin, two trematode Hbs: Paramphistomum epiclitum (Pe) and Gastrothylax crumenifer (Gc). As for HbA or SW Mb, the transition from heme to cobalt-porphyrin in the trematode Hbs leads to a large decrease in the oxygen affinity, with oxygen partial pressures for half saturation (P(50)) of 5 and 25 mm Hg at 37 degrees C for cobalt-Pe and cobalt-Gc, respectively. A critical parameter for Hb-based blood substitutes is the autoxidation rate; while both metals oxidize to an inactive state, we observed a decrease in the oxidation rate of over an order of magnitude for cobalt versus iron, for similar oxygen affinities. The time constants for autoxidation at 37 degrees C were 250 and 100 h for Pe and Gc, respectively.  (+info)

The influence of different food sources on cercarial production in Lymnaea truncatula experimentally infected with Digenea. (2/12)

Experimental infections of Lymnaea truncatula with a digenean species (Fasciola gigantica, F. hepatica, or Paramphistomum daubneyi) were performed under laboratory conditions to study the effect of four sources of food (microalgae, romaine lettuce, wheat germs, or modified Boray diet) on cercarial production. The mean number of F. hepatica, F. gigantica, or P. daubneyi cercariae was significantly greater when snail food was microalgae or Boray diet. The lowest cost prices for 100 metacercariae of F. hepatica (9.7-10.1 euros) were noted when algae of Boray diet were used as food for snails. In contrast, the highest prices (18.0-18.5 euros) were found in lettuce-reared snails. The choice of a source of food for breeding the intermediate hosts of F. hepatica and collecting metacercariae must take into account the importance of the commercial demand for metacercariae and will depend on the strategy the producer wishes to develop.  (+info)

Fasciola hepatica and Paramphistomum daubneyi: changes in prevalences of natural infections in cattle and in Lymnaea truncatula from central France over the past 12 years. (3/12)

A retrospective study was carried out over a 10- to 12-year period to analyse the changes in prevalences of natural fasciolosis and paramphistomosis among cattle and snails in central France, and to determine the causes which had induced these changes. The prevalences of natural fasciolosis in cattle increased from 1990 to 1993 (13.6% to 25.2%) and diminished afterwards up to 1999 (at 12.6%). Those of natural paramphistomosis showed a progressive increase between 1990 and 1999 (from 5.2 to 44.7%). The prevalences of natural infections and the numbers of free rediae counted in the snails (Lymnaea truncatula) infected with F. hepatica did not show any significant variations over time. By contrast, the prevalences of natural paramphistomosis in snails significantly increased from 1989 to 1996 and remained afterwards in the same range of values (3.7-5.3%), while the number of free rediae significantly increased up to 2000 (from a mean of 6.5 to 13.8 rediae per infected snail, respectively). Three hypotheses may explain the increase of paramphistomosis in cattle and snails: a better quality of diagnosis for the detection of P. daubneyi eggs in veterinary analysis laboratories, the use of specific molecules in the treatment of cattle fasciolosis since 1993, and the lack of an effective treatment up to now against cattle paramphistomosis. Since the objective of most farmers in central France is to obtain the highest antiparasitic efficiency with a single treatment of cattle per year, it is reasonable to assume that the prevalence of bovine paramphistomosis will continue to increase in the future.  (+info)

1H NMR study of the molecular structure and magnetic properties of the active site for the cyanomet complex of O2-avid hemoglobin from the trematode Paramphistomum epiclitum. (4/12)

The solution molecular and electronic structures of the active site in the extremely O2-avid hemoglobin from the trematode Paramphistomum epiclitum have been investigated by 1H NMR on the cyanomet form in order to elucidate the distal hydrogen-bonding to a ligated H-bond acceptor ligand. Comparison of the strengths of dipolar interactions in solution with the alternate crystal structures of methemoglobin establish that the solution structure of wild-type Hb more closely resembles the crystal structure of the recombinant wild-type than the true wild-type met-hemoglobin. The distal Tyr66(E7) is found oriented out of the heme pocket in solution as found in both crystal structures. Analysis of dipolar contacts, dipolar shift and paramagnetic relaxation establishes that the Tyr32(B10) hydrogen proton adopts an orientation that allows it to make a strong H-bond to the bound cyanide. The observation of a significant isotope effect on the heme methyl contact shifts confirms a strong contact between the Tyr32(B10) OH and the ligated cyanide. The quantitative determination of the orientation and anisotropies of the paramagnetic susceptibility tensor reveal that the cyanide is tilted approximately 10 degrees from the heme normal so as to avoid van der Waals overlap with the Tyr32(B10) Oeta. The pattern of heme contact shifts with large low-field shifts for 7-CH3 and 18-CH3 is shown to arise not from the 180 degrees rotation about the alpha-gamma-meso axis, but due to the approximately 45 degrees rotation of the axial His imidazole ring, relative to that in mammalian globins.  (+info)

Catadiscus pomaceae sp. n. (Trematoda, Paramphistomatidae) from Pomacea canaliculata (Lamarck, 1801) (Prosobranchia, Ampullariidae). (5/12)

Catadiscus pomaceae sp. n. from the intestine of the prosobranch mollusc Pomacea canaliculata (Lamarck, 1801), is described. The host snail was collected from a lenitic biotope belonging to the Riachuelo basin (Corrientes province, Argentina) during 1985-1986. So far the species of the genus Catadiscus Cohn, 1904 have been recorded in amphibians and reptiles. This is the first instance of a species of that genus parasitizing a mollusc.  (+info)

Report of Balanorchis anastrophus in Para State with surface topography by scanning electron microscopy. (6/12)

Balanorchis anastrophus Fischoeder, 1901, from the reticulum of Bos taurus is reported for the first time in the State of Para, Brazil. The surface topography as revealed by scanning electron microscopy is presented.  (+info)

Cotylophoron Travassosi sp. n. (Trematoda--Paramphistomidae) from cattle. (7/12)

A new species of the genus Cotylophoron (Trematoda--Paramphistomidae) --Cotylophoron travassosi sp. n.--is described. The measurements of the worm and its structures are compared with the valid known species.  (+info)

The hemoglobins of the trematodes Fasciola hepatica and Paramphistomum epiclitum: a molecular biological, physico-chemical, kinetic, and vaccination study. (8/12)

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