EPR study of the redox interactions in cytochrome c3 from Desulfovibrio vulgaris Miyazaki

We present a new examination of the EPR redox titration data for the tetraheme cytochrome c3 from Desulfovibrio vulgaris Miyazaki. Our analysis includes the contribution of the interaction potentials between the four redox sites and is based on the model previously developed for the study of cytochrome c3 from Desulfovibrio desulfuricans Norway. We observed, as for D. desulfuricans Norway cytochrome c3, that the conformation of the heme with the lowest redox potential, heme 4, is sensitive to the redox state of the heme with the highest potential, heme 1. However in D. vulgaris Miyazaki cytochrome c3 spectral simulations show that heme 4 is present in two conformational states which interconvert partially when heme 1 is reduced. The sets of redox parameters which satisfy the fitting procedure of the titration curves are in the following domain: -250 mV less than or equal to e41 less than or equal to -220 mV, -325 mV less than or equal to e2 less than or equal to -320 mV, -335 mV less than or equal to e3 less than or equal to -330 mV, -360 mV less than or equal to e4 less than or equal to -355 mV, -5 mV less than or equal to I12 less than or equal to 20 mV, -10 mV less than or equal to I13 less than or equal to 5 mV, -15 mV less than or equal to I23 less than or equal to -5 mV, -15 mV less than or equal to I24 less than or equal to -10 mV, -25 mV, less than or equal to I34 less than or equal to -15 mV. As in D. desulfuricans Norway cytochrome c3 the interactions are moderate. Simple electrostatic considerations suggest that these moderate values could be related to the large accessibility of the hemes to the solvent. Our work does not confirm the existence of a cooperative interaction between heme 2 and heme 3 which has been proposed on the basis of electrochemical measurements.     

Isolation and physiological study of an amylolytic strain of Lactobacillus plantarum

Summary An amylolytic lactic acid bacterium identified as Lactobacillus plantarum was isolated from cassava roots (Manihot esculenta var. Ngansa) during reting. The amylolytic enzyme synthesized was an extracellular -amylase with an optimum pH of 5.0 and an optimum temperature of 55° C. Cultured on starch, the strain displayed a growth rate of 0.43 h^–1, a biomass yield of 0.19 g·g^–1 and a lactate yield of 0.81 g·g^–1. The growth kinetics were similar on starch and glucose. Sufficient enzyme was synthesized and starch hydrolysis was not a limiting factor for growth. Biosynthesis of the enzyme was observed when the glucose concentration was less than 6.7 g·l^–1 and reached up to 4 IU·ml^–1 at the end of the fermentation. Offprint requests to: M. Raimbault     

Correlates and implications of breast-feeding practices in Bas Zaire

A sample of 1871 women having a child under 3 years old in Bas Zaire was studied to determine the correlates of breastfeeding practices and to examine the interrelationships among breastfeeding, contraceptive practices and desire for pregnancy. The methods of analysis applied were life table analysis and its multivariate extensions. Most of the findings in this analysis are consistent with current literature on the correlates of the duration of breastfeeding. Maternal education, economic status, age, parity, urban residence, pregnancy, and sex of the index child were significantly related to the length of breastfeeding. Among non-pregnant women, current desire for pregnancy was also related to breastfeeding status when the length of time since birth of the last child was taken into consideration. Rural women were reportedly ready for another pregnancy sooner after the birth of their last child than were urban women. Breastfeeding appears to be the most important means of contraceptive protection in the study population. The effective traditional method of extended postpartum abstinence is not widely prevalent, particularly among the urban sample, and indeed seems to be on the decline. The data presented here also suggest that breastfeeding pratices are changing in this area of Africa where little economic development has occurred in the past 20 years. This research suggests that if current trends continue, fertility levels are likely to increase significantly. The findings also indicate that Bas Zairian mothers want to space their births and for this reason may be receptive to family planning programs that use appropriate strategies.     

Long-term comparative effect of cholecystokinin and gastrin on mouse stomach, antrum, intestine, and exocrine pancreas

Mice were injected three times a day for 12 days with 300 micrograms/kg body weight of gastrin G17 or 37.5 Ivy dog U/kg body weight of CCK or saline. Other mice were also injected four times an hr for 1 hr with 7.5 micrograms/kg of gastrin, nine Ivy dog U/kg of CCK or saline; 1 hr before killing, they were injected with tritiated thymidine to evaluate the labelling indices in peptic, antral, duodenal, jejunal, and ileal mucosae. Four hours after the first injection of the two peptides, the peptic labelling indices increased while those of intestinal mucosa increased 8 hr after these injections. Long-term injections of CCK had a trophic effect on secretory cells of the digestive tract: the number of gastric zymogenic cells, Paneth cells, and the mucous cells of Brünner glands were hypertrophied. The pepsin, amylase, chymotrypsin, and lysozyme activities increased in stomach, exocrine pancreas, and intestine, respectively. Neither parietal cells nor intestinal enterocytes and hydrolase activities were affected. The trophic effect of long-term injections of gastrin is confirmed on parietal cells and exocrine pancreatic parenchyma and is demonstrated in Paneth cells. Confirming cytological results, pancreatic lipase and amylase activities and intestinal lysozyme activity were increased after gastrin. Although CCK and gastrin have a structural analogy, these two peptides did not affect the same cellular types. A specific action of CCK on the main secretory cells of the digestive mucosa is demonstrated.     

Characterization of Rhizobia from Ineffective Alfalfa Nodules: Ability to Nodulate Bean Plants [Phaseolus vulgaris (L.) Savi.]

This study was initiated to characterize Rhizobium isolates obtained from root nodules of ineffectively nodulated, field-grown alfalfa (Medicago sativa L.) plants. The purpose was to determine if these isolates possessed characteristics which would explain either their ineffectiveness in N₂ fixation or their apparent ability to tolerate the moderately acid soil conditions from which they originated. Isolates were characterized by analysis of growth rate, 39°C tolerance, acid production on conventional media, and symbiotic performance. All isolates were ineffective in N₂ fixation on alfalfa, and they contained one or more anomalous characteristics. These included either slow growth rate, lack of 39°C tolerance, or lack of acid production on conventional media. Infectiveness tests on a broad range of legumes revealed that the isolates formed root nodules on M. sativa, Medicago lupulina L., and Phaseolus vulgaris (L.) Savi. (common bean). These results provide evidence that, in some situations, ineffective nodulation of M. sativa in the field may be due to the presence of promiscuous, native Rhizobium species.     

Promoter mutations affecting divergent transcription in the Tn10 tetracycline resistance determinant

The tetracycline resistance determinant in transposon Tn10 consists of two genes, the tetA resistance gene and the tetR repressor gene, that are transcribed from divergent overlapping promoters. We determined the levels of pulse-labeled tet messenger RNA in Escherichia coli strains with the Tn10 tet genes on a multicopy plasmid. Addition of the inducer 5a,6-anhydrotetracycline results in a 270- to 430-fold increase in tetA mRNA and a 35- to 65-fold increase in tetR mRNA. As judged by the relative molar amounts of tetA and tetR mRNA synthesized under maximally inducing conditions, the tetA promoter (tetPA) is 7 to 11 times more active than the two tetR promoters (tetPR1 and tetPR2) combined. We characterized ten mutations in tetPA, including nine single-base-pair substitutions and a 30-base-pair deletion. All of the single-base-pair changes reduce the agreement with the consensus sequence for promoters recognized by E. coli RNA polymerase. Mutations in highly conserved nucleotides result in a 200- to 600-fold reduction in tetPA activity in vivo. Unexpectedly, tetPA mutations reduce by two- to fourfold the combined activity in vivo of tetPR1 and tetPR2, in spite of their locations outside the -35 and -10 regions of tetPR1 and tetPR2. For two tetPA mutations, the negative effect on tetPR activity was also demonstrated in tetR- tetPR-lacZ operon fusion strains, thus eliminating the possibility that it is due to variations in either plasmid copy-number or induction efficiency. The pleiotropic effects of tetPA mutations are discussed in terms of the expectation that the overlapping tet promoters compete for RNA polymerase.     

Insertion of a foreign nucleotide sequence into mitochondrial DNA causes senescence in Neurospora intermedia

The kalilo variants of Neurospora contain a cytoplasmic genetic factor that causes senescence. This factor is a 9.0 kb transposable element (kalDNA) that lacks nucleotide sequence homology with mtDNA and is inserted into the mitochondrial chromosome, often at sites located within the open reading frame in the intron-DNA of the mitochondrial 25S-rRNA gene. Genomes containing the "foreign" DNA insert accumulate during growth, and death occurs as the cells become deficient in functional large and small subunits of mitochondrial ribosomes. The kalDNA transposon may be an "activator" element that causes breaks in mtDNA. Nonsenescing [+] strains of Neurospora do not contain kalDNA.     

An HLA-C-specific DNA probe

Analysis of available nucleotide sequence data for class I HLA genes has established that the seventh intron is one of the gene regions which expresses the highest degree of locus specificity (the percentage sequence divergence between nonallelic genes minus the percentage sequence divergence between allelic genes). We have subcloned short DNA sequences including this region from the HLA-Cw3 gene. Two clones, pC250 and pC800, were tested by hybridizing them at high stringency to a panel of clones containing class I HLA genes. Under conditions permitting a strong hybridization signal with a C-locus gene, pC800 also expressed a weak but significant hybridization to other class I genes, while pC250 appeared to hybridize exclusively to the C-locus gene. Hybridization of the pC250 probe at high stringency to Hind III-digested genomic DNA from a panel of unrelated individuals and homozygous typing cell lines revealed a single band in all cases. However, equivalent hybridization against Eco RI-digested DNA revealed two hybridization bands, one at 7.9 kb which correlated with the serologically defined Cw5 and Cw8 alleles, and one at 7.6 kb which correlated with the Cw1, Cw2, Cw3, Cw4, Cw6, and Cw7 alleles.     

Fermentation procedure of a crude oil in continuous culture on seawater

Summary The crude oil was degraded (80%) in continuous culturing and non sterile conditions by a mixed bacteria community. The fermentation process relies on a step of pre-emulsification of the substrate before it is introduced into the reactor. The emulsification indispensable for degrading crude oil is performed by the mixed bacteria community during its growth on hydrocarbons. On the other hand, the use of an ultrafiltration device allows the obtention of high cell concentrations (7.6 g·l^-1) and high degradation rates.