Characterisation of the enzyme activities involved in the valine biosynthetic pathway in a valine-producing strain of Corynebacterium glutamicum.

The enzyme activities of the valine biosynthetic pathway and their regulation have been studied in the valine-producing strain, Corynebacterium glutamicum 13032DeltailvApJC1ilvBNCD. In this micro-organism, this pathway might involve up to five enzyme activities: acetohydroxy acid synthase (AHAS), acetohydroxy acid isomeroreductase (AHAIR), dihydroxyacid dehydratase and transaminases B and C. For each enzyme, kinetic parameters (optimal temperature, optimal pH and affinity for substrates) were determined. The first enzyme of the pathway, AHAS, was shown to exhibit a weak affinity for pyruvate (K(m)=8.3 mM). It appeared that valine and leucine inhibited the three first steps of the pathway (AHAS, AHAIR and DHAD). Moreover, the AHAS activity was inhibited by isoleucine. Considering the kinetic data collected during this work, AHAS would be a key enzyme for further strain improvement intending to increase the valine production by C. glutamicum.

Sub-Doppler resolution limited Lamb-dip spectroscopy of NO with a quantum cascade distributed feedback laser.

A quantum cascade distributed feedback laser operating at 5.2 microm is used to obtain sub-Doppler resolution limited saturation features in a Lamb-dip experiment on the R(13.5)1/2 and R(13.5)3/2 transitions of NO. The dips appear as transmission spikes with full widths of ~ 4.3 MHz. At this resolution the 73 MHz _-doubling of the R(13.5)3/2 line, which is normally obscured by the 130 MHz Doppler broadening, is easily resolved.

A method for the determination of pyruvate carboxylase activity during the glutamic acid fermentation with Corynebacterium glutamicum.

A discontinuous lactate dehydrogenase coupled assay is described for the evaluation of the pyruvate carboxylase activity (Pc, EC 6.4.1.1) in a glutamate overproducing strain of Corynebacterium glutamicum. After an initial permeabilisation period of the cells, the method consisted of the fluorometric determination of the remaining pyruvate level after transformation into oxaloacetate by the endogenous Pc. The assay was demonstrated to be powerful and enabled the determination of the C. glutamicum Pc activity grown on different carbon sources. Besides, this method was used to assay Pc activity in C. glutamicum 2262 during a temperature triggered glutamate producing process with biotin excess or limitation.

Importance of phosphoenolpyruvate carboxylase of Corynebacterium glutamicum during the temperature triggered glutamic acid fermentation.

To give clues about the respective importance of phosphoenol-pyruvate carboxylase (PEPc) and pyruvate carboxylase (Pc) in Corynebacterium glutamicum metabolism during a temperature triggered glutamic acid fermentation, PEPc activity was genetically amplified and Pc activity was suppressed by biotin limitation in the culture medium. In absence of Pc activity, glutamate production was dramatically reduced whereas lactate excretion was strongly increased. Whereas PEPc amplification in excess of biotin (4 mg/L) only slightly modified the cell kinetics, under biotin limiting conditions this amplification strongly improved the glutamate production (4 microg/L). When Pc was absent, PEPc activity was sufficient to allow up to 70% of the maximal glutamate production rate and seemed to have an important anaplerotic role, especially at the beginning of the production phase. In contrast, Pc was predominant during the remainder of the glutamate fermentation.

Observation of Delta|k - l | = 3 Transitions in the nu3 Band of H3 O+

Although the vibration-rotation spectrum of H3 O+ has been studied extensively, there has been no experimental information on the value of the C rotational constant because of the absence of any observed Delta|k - l | not equal 0 forbidden transitions. However, as pointed out by Verhoeve et al. in their far-infrared spectroscopic work [P. Verhoeve, M. Versluis, J. J. Ter Meulen, W. L. Meerts, and A. Dynamus, Chem. Phys. Lett. 161, 195-201 (1989)], a near degeneracy exists between some (J , 0)+ and (J , 3)- ground state rotation-inversion levels, which causes sizable shifts in these levels due to off-diagonal centrifugal distortion. These shifts were observed in the ground state combination differences of the nu3 fundamental transitions. We have observed 11 forbidden Delta|k - l | = 3 transitions to the nu3 band induced by the mixing in the ground state and involving the J = 7, 9, and 11 levels, and determined the energy difference between different K levels, the C rotational constant, and the off-diagonal centrifugal distortion mixing coefficient.

Autonomic blockade and the cardiovascular and catecholamine response to electroshock.

From a study on the interrelationship between electroshock-induced convulsions, autonomic function, catecholamines, and cardiovascular homeostasis in dogs, the authors found that: (1) the asystole of electroshock (ES) was significnatly prolonged by high spinal anesthesia but not by relative alpha- or beta-adrenergic blockade; (2) increased levels of circulating catecholamines were solely responsible for the marked hypertensive response to ES, since the pressor effect could be blocked by preventing the release of catecholamines with high spinal anesthesia or by inhibiting alpha-adrenergic receptors with phenoxybenzamine; (3) the adrenal medulla appeared to be the source of most of the ES-induced increase in circulating catecholamines; (4) the asystole and arrhythmias of ES were a cholinergic effect, since they were blocked by atropine; (5) there was a dose-response relationship between the coulombs of electricity administered and the catecholamine and cardiovascular responses; and (6) that the adverse cardiovascular effects of ES therapy could be ameliorated pharmacologically.