encoded as a group on chromosome 4q22. The Class IV isozyme is expressed in epit
ID: 200737 • Letter: E
Question
encoded as a group on chromosome 4q22. The Class IV isozyme is expressed in epithelial tissues, such as the mucosal lining of the stomach and upper intestines. There is evidence that it is involved in the oxidation of retinol to retinal, the precursor of retinoic acid, the form of vitamin A that serves as a signaling agent in regulation of gene expression involved in growth, development, and epithelial maintenance. The active isomers of retinoic acid, which bind to nuclear receptor prot are 4. In addition to the Class I liver ADH above, there are five other classes of human ADH. All are COOH HyC all-trans-retinoic acid 9-cis-retinoic acid Class IV ADH follows a Bi Bi single displacement reaction mechanism with turnover numbers of 67 min (all-trans-retinol), 475 min (9-cis-retinol), and 2570 min (ethanol). Quenching of the florescence of a tryptophan residue has been used to monitor binding of substrates to Class IV ADH yielding the data in the Table below. The binding reactions contained 56 nM enzyme in 0.1 M sodium phosphate, pH 75, 2% (v/v) acetonitrile, and 0.02% v/v) Tween 80 and were run at 25°C. NAD ethanol all-trans-retinol cis-9-retinol 0.0278 0.0457 0.0582 0.0674 0.0744 0.00061 0.00151 10 20 30 40 50 0.0512 10 20 50 100 0.0151 200 500 0.0512 0.0080 200 500 0.0731 00298 300.0931 1-0.00582-1 -40 I 0-0853 0.0985 0.0269 000 0.00582 1000 0.07315000 0.01362 40 50Explanation / Answer
The results clearly indicate that class iv ADH follows an ordered rapid equilibrium reaction with regard to its substrate like the class I ADH. A single ternary complex acts as a substrate for retinol reduction from its parent compound. When double-reciprocal plots for oxidation and reduction is used, the graph clearly shows the approaching of slope towards 0 signifying a rapid equilibrium state. Also, the fact that the product NAD+ does not inhibit retinal, confirms that the reaction is of rapid order equilibrium and forms a retinol-nadh-enzyme complex. This is a non conpetitive binding reaction that is not dependent on product concentration.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.