A Del Corso

THIOL DEPENDENT OXIDATION OF ENZYMES : THE LAST CHANCE AGAINST OXIDATIVE STRESS

1. A survey of known effects of oxidized thiols on enzyme activity reveals a potential concerted action on metabolic pathways determining an impairment of anabolic reduction processes and an activation of the oxidative arm of the hexose monophosphate shunt. Thus it appears that, following oxidative stress, the increase of disulphides may act in restoring a reduced state in the cell by specifically channelling the metabolic energy flux.

Chaperone-like features of bovine serum albumin: a comparison with α-crystallin

Abstract.The chaperone behaviour of bovine serum albumin was compared with that of α-crystallin. The chaperone activity was assessed by measuring: (i) the ability to antagonize protein aggregation induced by heat; (ii) the capability to protect the activity of thermally stressed enzymes and (iii) the effectiveness in assisting the functional recovery of chemically denatured sorbitol dehydrogenase. Despite the lack of structural analogies, both proteins show several functional similarities in preventing inactivation of thermally stressed enzymes and in reactivating chemically denatured sorbitol dehydrogenase. As with α-crystallin, the chaperone action of bovine serum albumin appears to be ATP independent. Bovine serum albumin appears significantly less effective than α-crystallin only in preventing thermally induced protein aggregation. A possible relationship between chaperone function and structural organization is proposed. Together, our results indicate that bovine serum albumin acts as a molecular chaperone and that, for its particular distribution, can be included in the extracellular chaperone family.

Alpha-crystallin: an ATP-independent complete molecular chaperone toward sorbitol dehydrogenase

Abstract.α-Crystallin, the major component of the vertebrate lens, is known to interact with proteins undergoing denaturation and to protect them from aggregation phenomena. Bovine lens sorbitol dehydrogenase (SDH) was previously shown to be completely protected by α-crystallin from thermally induced aggregation and inactivation. Here we report that α-crystallin, in the presence of the SDH pyridine cofactor NAD(H), can exert a remarkable chaperone action by favoring the recovery of the enzyme activity from chemically denaturated SDH up to 77%. Indeed, even in the absence of the cofactor, α-crystallin present at a ratio with SDH of 20:1 (w:w) allows a recovery of 35% of the enzyme activity. The effect of ATP in enhancing α-crystallin-promoted SDH renaturation appears to be both nonspecific and to not involve hydrolysis phenomena, thus confirming that the chaperone action of α-crystallin is not dependent on ATP as energy donor.

Aldehyde reductase activity in the antennae of Helicoverpa armigera.

In the present study, we identified two aldehyde reductase activities in the antennae of Helicoverpa species, NADH and NADPH‐dependent activity. We expressed one of these proteins of H. armigera, aldo‐keto reductase (AKR), which bears 56% identity to bovine aldose reductase, displays a NADPH‐dependent activity and is mainly expressed in the antennae of adults. Whole‐mount immunostaining showed that the enzyme is concentrated in the cells at the base of chemosensilla and in the nerves. The enzyme activity of H. armigera AKR is markedly different from those of mammalian enzymes. The best substrates are linear aliphatic aldehydes of 8–10 carbon atoms, but not hydroxyaldehydes. Both pheromone components of H. armigera, which are unsaturated aldehydes of 16 carbons, are very poor substrates. Unlike mammalian AKRs, the H. armigera enzyme is weakly affected by common inhibitors and exhibits a different behaviour from the action of thiols. A model of the enzyme suggests that the four cysteines are in their reduced form, as are the seven cysteines of mammalian enzymes. The occurrence of orthologous proteins in other insect species, that do not use aldehydes as pheromones, excludes the possibility of classifying this enzyme among the pheromone‐degrading enzymes, as has been previously described in other insect species.

Liver purine nucleoside phosphorylase in Camelus dromedarius: purification and properties.

1. Purine nucleoside phosphorylase (purine nucleoside:orthophosphate ribosyl transferase, EC 2.4.2.1) was purified to electrophoretic homogeneity from the liver of Camelus dromedarius. 2. The enzyme appears to be a dimer with a 44,000 subunit mol. wt and displays non-linear kinetics with concave downward curvature in double reciprocal plots with respect to both inosine and orthophosphate as variable substrates. 3. The effect of thiol compounds on the enzyme activity and of pH on kinetic parameters is reported.