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A decapeptide X has a molecular weight of 796. Complete hydrolysis yields alanine (MW 75), phenylalanine, and glycine as products. Glycine accounts for 47% of the total weight of all hydrolysis products. Let a = total number of alanine and phenylalanine units in X, and b = number of glycine units in X. Find (b - a).

1. 1
2. 2
3. 3
4. 4

Correct answer: 2

Solution

Total hydrolysis product weight = 796 + 9*18 = 958. Glycine contribution = 0.47 * 958 = 450.26 ≈ 450. b = 450/75 = 6. a = 10 - 6 = 4. b - a = 6 - 4 = 2.

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