Cysteine entrapping

The nucleophilic reactivity of cysteine has been exploited in Michael reactions with quinones. One example is a water-soluble naphthoquinone, which has been entrapped in chlorophyll-containing vesicles in order to study light-induced electron transfer through a membrane from glutathione to the quinone (Fore, 1983). Another example is an asymmetrical vesicle membrane made of a cysteine quinone carboxylate bolaamphiphile, where all the quinone is localized on the outer surface of the vesicle (see Scheme 7.2.6 Scheme 9.5.1). 

Figure 5. Effect of temperature on the stability of immobilized cells. The gel-entrapped dried cells (a) were incubated in O.OIM potassium phosphate buffer, pH 7.0, for 3 hr

Figure 8. Synthesis of CoA on an immobilized cell column. (A) Single column system a substrate mixture composed of sodium pantotheruite (2,5 fimol/mL), cysteine (10 nmoUmL), ATP (15 fxmoHmL), magnesium sulfate (10 imol/mL), potassium phosphate buffer, pH 6.5 (150 nmol/mL), and sodium laurylsulfate (1 mg/mL) teas applied to a column (1 X 20 cm) of gel-entrapped dried cells. The reaction was carried out at 34°C with a flow rate of SV = 0.1-O.2 hr h (B) Separated column system a substrate mixture composed of sodium pantothenate (2.5 /imol/mL), ATP (7.5 ixmol/mL), magnesium sulfate (10 nmol/mL), potassium phospate buffer, pH 6.5 (150 fimol/mL), and sodium laurylsulfate (1 mg/mL) was applied to the top of the column (1 X 10 cm). Solution (about 20 mh) passed through the column at a flow rate of SV = 0.1-0.2 hr t was collected every day. To the solution (20 mL), 200 nmol cysteine and 150 fimol ATP were added, which was then reacted at the bottom of the column (1 X 10 cm) with a flow rate of SV = 0.1-0.2 hr to yield CoA. The reaction temperature was 34°C. Consumption of pantothenic acid was checked both at the top (b) and bottom (a) columns.

In this chapter, two subjects of our study were described. One was concerned with the catalysis by enzymes entrapped in water pools and photomerization at the level of a biomembrane model in vivo. Based on the study of the activity of yeast HK in the water pools, the activity of HK can be seen in noncharged polyoxyethylene mantles with relatively low micropolarity in which almost all the water molecules are bound up with EO chains. This suggests that yeast HK can work more actively in the vicinity of mitochondrial membranes in vivo. The photomerization of cysteine in the water pool with UV irradiation shows that cysteine is easily converted into cystine with lower Wg. This suggests that active oxygen is generated at the interface of the biomembrane rather than in bulk aqueous solution in vivo and SH groups of proteins in the cell membrane are oxidized similarly with UV irradiation. 

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