Studies on the inactivation of glyceraldehyde-3-phosphate dehydrogenase by methylglyoxal

Glyceraldehyde-3-P dehydrogenase (E.C. 1.2.1.12) from rabbit muscle is rapidly inactivated by methylglyoxal following pseudo first-order kinetics. Substrate, as well as inorganic phosphate, affords protection, whereas NAD+ is ineffective. The arginine residue implicated in the reaction is probably the anion binding site of the phosphate group of the substrate.

Studies on the interaction of fructose 1,6-P2 aldolase with methylglyoxal

Reaction of rabbit muscle fructose 1,6-P2 aldolase with methylglyoxal results in a biphasic loss of activity. The kinetics of the initial rapid phase are first order with respect to the inhibitor. Dihydroxyacetone phosphate and fructose 1,6 bisphosphate afford complete protection whereas inorganic phosphate provides only a partial protection against inactivation. The treatment with methylglyoxal modifies the aldolase ability to bind D-Ga3P and DHAP. Loss of activity correlates with the modification of 1.7 arginine residues but data suggest that probably one of these arginine residues is essential. A likely role of this residue could be its interaction with the C1 negatively charged phosphate binding site of the enzyme.

Comparative aspects of the inactivation of fructose 1,6 bisphosphate aldolase by D- and l-glyceraldehyde 3-phosphate

Fructose 1,6-bisphosphate aldolase inactivation by L- and D-glyceraldehyde 3-phosphate (Ga 3-P) obeys pseudo first-order kinetics. L-Ga 3-P is much more effective than the D-isomer: the Ki values obtained are 0.032 mM and 0.54 mM respectively. Kinetic analysis suggests that one residue of the active center region is involved in the inactivation mechanism: specifically, a cysteine residue appears to be responsible for the initial inactivation by L-Ga 3-P. Lysine and arginine residues become involved at further steps of the inactivation mechanism. No correlation between loss of thiol groups and decay of catalytic activity was observed for the enzyme treated with D-Ga 3-P. The role of lysine and arginine residues in this reaction is discussed.

Skin potential and EMG changes induced by cutaneous electrical stimulation. I. Normal man in arousing and non-arousing environment

Skin potential and EMG responses induced in normal man by electrical stimuli applied to the skin were recorded in the four limbs in order to study somato-sympathetic and somato-motor reflexes. Different patterns of responses were observed in different conditions: alarm, habituation, sensitization and arousal. During alarm, sensitization and arousal, the responses were present in the four limbs; during habituation, the responses were only present in the stimulated and in the contralateral limb. Three sensory thresholds to cutaneous electrical stimulation were identified in habituated subjects: tactile, tingling and pain. Cutaneous and EMG responses appeared at tingling threshold. A relationship between skin potential level and skin potential response was observed.

Skin potential and EMG changes induced by cutaneous electrical stimulation. II. Subjects with reflex sympathetic dystrophies

In a group of patients suffering from reflex sympathetic dystrophies, the skin potential and EMG responses induced by electrical stimuli applied to the skin were recorded in the four limbs in order to study somato-sympathetic and somato-motor reflexes. In most patients, the amplitude, delay and shape of the cutaneous responses as well as the pattern of the EMG responses were different from those observed in normal subjects. In particular, it was possible to correlate the pattern of the cutaneous and muscular responses with the severity of the disease. The cutaneous sensory thresholds to electrical stimuli (tactile, tingling and pain threshold) showed different values in the dystrophic and in the contralateral limb. In all patients, a block of the sympathetic chain ipsilateral to the dystrophic limb was performed with local anesthetics. 1 h after the block, the cutaneous responses disappeared not only in the blocked limb but also in the contralateral limb. 48 h after the block, muscular and cutaneous responses as well as sensory thresholds showed a pattern similar to that observed in normal subjects. These findings show that the sympathetic block provides a resetting of the sensory thresholds and reflexes.

D,L-Glyceraldehyde 3-phosphate breakdown in the presence of selenalysine

Selenalysine is more effective than lysine both on glyceraldehyde 3-P transformation into methylglyoxal and on subsequent methylglyoxal polymerization.