# DBT JRF 2020 — Question 136

Exam: DBT JRF 2020 · Section: B · Topic: Biotechnology · Difficulty: Hard

## Question

The artificial sweetener, aspartame, is enzymatically produced using

## Options

- **A.** rennin
- **B.** Thermolysin
- **C.** β-galactosidase
- **D.** lipase

## Answer

Option B

## Explanation

Aspartame ( $\alpha$ -L-aspartyl-L-phenylalanine-1-methyl ester) is an artificial sweetener ~200× sweeter than sucrose. Chemical production: N-protected (e.g. Z-Asp or Cbz-Asp) aspartic acid + L-phenylalanine methyl ester (L-PheOMe), coupled by Thermolysin. Thermolysin (EC 3.4.24.27) is a thermostable zinc-metalloendoprotease from Bacillus thermoproteolyticus that exhibits remarkable synthetic (condensation) activity in organic solvents or biphasic systems. Advantages: (1) Excellent stereoselectivity — produces ONLY the L-L stereoisomer (the sweet one; L-D and D-L isomers are bitter/tasteless); (2) Thermostability; (3) No unwanted side reactions. Rennin (chymosin) — milk coagulation; $\beta$ -galactosidase — lactose hydrolysis; Lipase — fat hydrolysis.

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