Exogenous NADPH

CL produced in the presence of exogenous NADPH or NADH, which has been studied in Refs. [97,100], may originate from other sources than superoxide generation [90]. In our opinion [98], the data obtained on the basis lucigenin CL measurement, especially with the use of small lucigenin concentrations provide the reliable estimate of superoxide concentration while the use of ESR spin technique underestimates it, particularly in vascular tissue and cells (see Chapter 32). 

Antibodies to iTOR Rabbits were immunized with the enzyme isolated from prolamellar bodies of 7-day-old etiolated barley leaves and purified by chromatography on DEAE-cellulose in the presence of exogenous NADPH and protoohlorophyllide (Pchlde) /5/ For ELISA, either rabbit antiserum diluted in the ratio of 1 8 (Pig.l) or the fraction of immunoglobulin a isolated from the antiserum on DEAE-cellu-lose 6ind diluted several times (Pig. 2) were used. 

In earlier studies, we have tried to assess the possible role of NADPH in the mechanism action of LH in this model system. Our early results indicated that it might be part of the mechanism. The addition of exogenous NADPH led to increase in mass of the steroid produced in incubating corpora lutea slices (3). As the work progressed, however, results began to appear which indicated a difference in the action of exogenous NADPH and LH. 

When both parameters of steroid s3mthesis were assessed (the increase in mass of progesterone and the incorporation of l C), it was found that exogenous NADPH increased the mass of steroid produced without a concomitant increase in the incorporation of LH, on the other hand, increased... 

Although these results st gest the LH does not act via NADPH, they are not conclusive since it is not known if the addition of exogenous NADPH is equivalent to increasing the endogenous concentration of this cofactor. 

The level of a particular enzyme involved in xenobiotic metabolism can obviously affect the extent of metabolism by that enzyme. Again, competition may play a part if endogenous and exogenous substrates are both metabolized by an enzyme, as is the case with some of the forms of cytochromes P-450, which metabolize steroids, or NADPH cytochrome P-450 reductase and cytochrome b5 reductase, which are also involved in heme catabolism and fatty acid metabolism, respectively. 

However, with certain secondary hydroxylamines, P-450, too, can catalyze transformation to nitrones. Thus, incubation of N,N-( 1 -phcnylcyclobutyljbenzyl hydroxylamine with P-450 2B1 in the presence of NADPH-cytochrome P-450 reductase and NADPH has been demonstrated to trigger nitrone 36 formation with Km = 48 pM by direct oxidation of the N-hydroxy compound exogenous catalase did not change the amount of product generated55. 

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