The study of a French family with two duplicated C4A haplotypes

Summary The finding of two duplicated C4A haplotypes in a normal French family led to a detailed study of their C4 polymorphism. The father had an extremely rare A^*6A^*11, B^* QO haplotype inherited by all of his children and the mother had the more common A^*3A^*2, B^*QO haplotype. Two HLA identical daughters only have four C4A alleles. The father's A11 allotype expresses Ch: 1 (Chido) rather than Rg:1 (Rodgers) and represents a new Ch phenotype Ch: 1,-2,-3,-4,-5,-6. In order to clarify the genetic background in this unusual family, DNA studies of restriction fragment length polymorphisms (RFLPs) were undertake. The father's rare haplotype, which expresses two C4A allotypes, results from a long and a short C4 gene normally associated with the A^*6, B^*1 that also exhibits the BglII RFLP. As it travels in an extended MHC haplotype HLA A2, B57 (17), C2^*C, BF^*S, DR7 that is most frequently associated with A^*6, B^*1, we postulate that the short C4B has been converted in the chain region to a C4A gene which produces a C4A protein. This report of a short C4A gene is the first example in the complex polymorphism of C4.     

Wolinella succinogenes fumarate reductase contains a dihaem cytochrome b

The fumarate reductase operon of Wolinella succinogenes is made up of three structural genes (frd-CAB). The frdC gene was located next to the promoter region and identified as the cytochrome b structural gene encoding 256 amino acid residues. The N-terminal amino acid sequences of seven fragments derived from the cytochrome b moiety of the enzyme all mapped within the frdC gene. This suggested that the enzyme contained only one species of cytochrome b. Re-evaluation of earlier measurements of subunit composition, haem B content and molecular weight led to the conclusion that the enzyme contained one molecule of cytochrome b with two haem B groups. The hydropathy plot of the amino acid sequence predicted five membrane-spanning hydrophobic segments, the first four of which contained a single histidine residue each. These residues could form the axial ligands to the two haem B groups. FrdC was found to be homologous with the cytochrome b (SdhC) of the Bacillus subtilis succinate dehydrogenase, but not with the hydrophobic subunits of the fumarate reductase or succinate dehydrogenase of Escherichia coli.     

Effect of positive redox potentials (>+400mV) on the expression of anaerobic respiratory enzymes in Escherichia coli

The expression of fumarate reductase and other enzymes of anaerobic respiration in Escherichia coli was studied as a function of the redox potential (Eh) in the medium. Redox potentials up to +300 mV allowed full expression of fumarate reductase (frd) genes. Higher values resulted in decreased expression. The relationship between Eh and expression of frd could be approximated by the Nernst equation, assuming a redox couple with a midpoint potential Eo' = +400 mV to 440 mV. At Eh values greater than +510 mV (generated anaerobically by hexacyanoferrate(III] the degree of repression was the same as that obtained by O2. Hexacyanoferrate(III) also caused decreased activities of dimethylsulphoxide (DMSO), nitrite and nitrate reductases. Since expression of these enzymes depends on FNR, the gene activator of anaerobic respiratory genes, it is suggested that the function of FNR is controlled by a redox couple of Eo' = +400 mV to 440 mV.     

Diurnal periodicity of chalcone-synthase activity during the development of oat primary leaves

Chalcone-synthase (CHS) activity was followed during the development of primary leaves of oat (Avena sativa L.) seedlings grown under different illumination conditions. Continuous darkness and continuous light resulted in similar time courses of enzyme activity. The maximum of CHS activity in etiolated leaves was delayed by 1 d and reached about half the level of that of light-grown leaves. In seedlings grown under defined light-dark cycles a diurnal rhythm of CHS activity and its protein level was observed which followed the rhythm of CHS-mRNA translational activity (Knogge et al. 1986). This rhythm persisted in continuous light after a short-term pre-exposure to the light-dark cycle but not in continuous darkness.Abbreviations CHS chalcone synthase - PAL phenylalanine ammonio lyase Financial support by the Deutsche Forschungsgemeinschaft is gratefully acknowledged (G.W., We 630/9-7; We 630/10-1). Thanks are given to Dr. St. Kellam (Department of Plant Microbiological Sciences, University of Canterbury, New Zealand) for correcting the English.     

Respiratory mechanics in mechanically ventilated patients with respiratory failure

In 11 mechanically ventilated patients, respiratory mechanics were measured 1) during constant flow inflation and 2) following end-inflation airway occlusion, as proposed in model analysis (J. Appl. Physiol. 58: 1840-1848, 1985. During the latter part of inflation, the relationship between driving pressure and lung volume change was linear, allowing determination of static respiratory elastance (Ers) and resistance (RT). The latter represents in each patient the maximum resistance value that can obtain with the prevailing time constant inhomogeneity. Following occlusion, Ers and RT were also obtained along with RT (min) which represents a minimum, i.e., resistance value that would obtain in the absence of time constant inhomogeneity. A discrepancy between inflation and occlusion Ers and RT was found only in the three patients without positive end-expiratory pressure, and could be attributed to recruitment of lung units during inflation. In all instances Ers and RT were higher than normal. RT(min) was lower in all patients than the corresponding values of RT, indicating that resistance was frequency dependent due to time constant inequalities. Changes in inflation rate did not affect Ers, while RT increased with increasing flow.     

Respiratory responses to ventilatory loading following low cervical spinal cord injury

This study compared the respiratory responses to ventilatory loading in 8 normal subjects and 11 quadriplegic patients with low cervical spinal cord transection. Progressive hypercapnia was produced by rebreathing. Rebreathing trials were carried out with no added load and with inspiratory resistive loads of 5 and 16 cmH2O. l-1 X s. Measurements were made of ventilation and of diaphragmatic electromyographic activity. Base-line hypercapnic ventilatory responses were significantly lower than normal in the quadriplegic patients, but the effects of resistive loading on the ventilatory responses were comparable in the two groups. The change in peak moving-average diaphragmatic electrical activity (DI peak) for a given change in CO2 partial pressure (PCO2) and DI peak at PCO2 55 Torr increased significantly with resistive loading both in the normal subjects and the quadriplegic patients. In the normal subjects, but not in the quadriplegic patients, inspiratory duration increased progressively with increasing resistance. The increase in DI peak during ventilatory loading in the normal subjects was a consequence of inspiratory prolongation. In contrast, in the quadriplegic patients during breathing against the larger resistive load, there was a significant increase in the average rate of rise (DI peak divided by the time from onset to peak) of diaphragmatic activity. The change in DI rate of rise for a given change in PCO2 increased to 137 +/- 13% (SE), and the DI rate of rise at PCO2 55 Torr increased to 128 +/- 8% (SE) of control values. These results indicate that compensatory increases in diaphragmatic activation during ventilatory loading occur in quadriplegic patients in whom afferent feedback from rib cage receptors is disrupted.     

Interrupter technique for measurement of respiratory mechanics in anesthetized humans

Flow (V), volume (V), and tracheal pressure (Ptr) were measured throughout a series of brief (100 ms) interruptions of expiratory V in six patients during anesthesia (halothane-N2O) and anesthesia-paralysis (succinylcholine). For the latter part of spontaneous expiration and throughout passive deflation during muscle paralysis, a plateau in postinterruption Ptr was observed, indicating respiratory muscle relaxation. Under these conditions, passive elastance of the total respiratory system (Ers) was determined as the plateau in postinterruption Ptr divided by the corresponding V. The pressure-flow relationship of the total system was determined by plotting the plateau in Ptr during interruption against the immediately preceding V. Ers averaged 23.5 +/- 1.9 (SD) cmH2O X l-1 during anesthesia and 25.5 +/- 5.4 cmH2O X l-1 during anesthesia-paralysis. Corresponding values of total respiratory system resistance were 2.0 +/- 0.8 and 1.9 +/- 0.6 cmH2O X l-1 X s, respectively. Respiratory mechanics determined during anesthesia paralysis using the single-breath method (W.A. Zin, L. D. Pengelly, and J. Milic-Emili, J. Appl. Physiol. 52: 1266-1271, 1982) were also similar. Early in spontaneous expiration, however, Ptr increased progressively during the period of interruption, reflecting the presence of gradually decreasing antagonistic (postinspiratory) pressure of the inspiratory muscles. In conclusion, the interrupter technique allows for simultaneous determination of the passive elastic as well as flow-resistive properties of the total respiratory system. The presence of a plateau in postinterruption Ptr may be employed as a useful and simple criterion to confirm the presence of respiratory muscle relaxation.     

Low-potential cytochrome b as an essential electron-transport component of menaquinone reduction by formate in Vibrio succinogenes

Incorporation of the electron-transport enzymes of Vibrio succinogenes into liposomes was used to investigate the question of whether, in this organism, a cytochrome b is involved in electron transport from formate to fumarate on the formate side of menaquinone. (1) Formate dehydrogenase lacking cytochrome b was prepared by splitting the cytochrome from the formate dehydrogenase complex. The enzyme consisted of two different subunits (M_r 110 000 and 20 000), catalyzed the reduction of 2,3-dimethyl-1,4-naphthoquinone by formate, and could be incorporated into liposomes. (2) The modified enzyme did not restore electron transport from formate to fumarate when incorporated into liposomes together with vitamin K-1 (instead of menaquinone) and fumarate reductase complex. In contrast, restoration was observed in liposomes that contained formate dehydrogenase with cytochrome b (E_m = ?224 mV), in addition to the subunits mentioned above (formate dehydrogenase complex). (3) In the liposomes containing formate dehydrogenase complex and fumarate reductase complex, the response of the cytochrome b of the formate dehydrogenase complex was consistent with its interaction on the formate side of menaquinone in a linear sequence of the components. The low-potential cytochrome b associated with fumarate reductase complex was not reducible by formate under any condition. It is concluded that the low-potential cytochrome b of the formate dehydrogenase complex is an essential component in the electron transport from formate to menaquinone. The low-potential cytochrome b of the fumarate reductase complex could not replace the former cytochrome in restoring electron-transport activity.