Question

Which one of the following is NOT an endogenous opioid peptide?

• A. met enkephalin
• B. leu enkephalin
• C. dynorphin
• D. beta lipotropin

Answer 1

The Correct Option is D

To determine which of the given options is not an endogenous opioid peptide, we need to understand what endogenous opioid peptides are. Endogenous opioids are naturally occurring molecules in the body that bind to opioid receptors to regulate pain, reward, and addictive behaviors. They are classified into several groups, mainly:

• Enkephalins: These include met-enkephalin and leu-enkephalin.
• Dynorphins: These are another class of endogenous peptides. 
• Endorphins: These include beta-endorphin.

Now, analyzing each option:

1. Met-enkephalin: It is a type of enkephalin, which is an endogenous opioid peptide.
2. Leu-enkephalin: This is also a type of enkephalin, classifying it as an endogenous opioid peptide.
3. Dynorphin: As part of the dynorphin family, it is an endogenous opioid peptide.
4. Beta-lipotropin: Although associated with the release of endorphins, beta-lipotropin itself is not classified as an opioid peptide. It is a precursor protein that can be processed into several different products, including beta-endorphin, which is an opioid peptide. However, beta-lipotropin itself is not considered an endogenous opioid peptide.

Therefore, the correct answer is \(\text{beta-lipotropin}\), as it is not directly an endogenous opioid peptide.