Which end does beta amylase cleave from?

[anondukie]

There is so much conflicting information on the net that I'm thoroughly confused. Intuitively, it makes sense that it would begin at the reducing end (the one with the free anomeric C) but most of the online sources I've looked at state that it cleaves at the non-reducing end. Can someone please shed light on this discrepancy?
Thank you!

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[Astra]

Beta amylase cleaves amylose at the reducing end of the polymer (the end with the free anomeric carbon); and it yields maltose


https://upload.wikimedia.org/wikibooks/en/e/e7/Starch-breakdown-sites.jpg

 

[aldol16]

Beta amylase cleaves amylose at the reducing end of the polymer (the end with the free anomeric carbon); and it yields maltose

Incorrect. Think about the implications of this. If it only cleaves at the reducing end and there is only one reducing end per glycogen molecule, this would work really slowly and would be terribly inefficient. In fact, beta amylase cleaves at a non-reducing end and contains recognition sites specifically for a non-reducing end.

http://onlinelibrary.wiley.com/doi/10.1016/0014-5793(70)80052-7/abstract
http://www.sciencedirect.com/science/article/pii/S0969212601002209
http://www.sciencedirect.com/science/article/pii/S0008621500852428

 

[Astra]

Incorrect. Think about the implications of this. If it only cleaves at the reducing end and there is only one reducing end per glycogen molecule, this would work really slowly and would be terribly inefficient. In fact, beta amylase cleaves at a non-reducing end and contains recognition sites specifically for a non-reducing end.

http://onlinelibrary.wiley.com/doi/10.1016/0014-5793(70)80052-7/abstract
http://www.sciencedirect.com/science/article/pii/S0969212601002209
http://www.sciencedirect.com/science/article/pii/S0008621500852428

That makes sense.

Sigh. Another mistake in the Kaplan book

 

[anondukie]

Aldol, would it make sense to say that it begins at the reducing end and then makes no distinction? Also, thanks for the prompt reply!

 

[aldol16]

Aldol, would it make sense to say that it begins at the reducing end and then makes no distinction? Also, thanks for the prompt reply!

No - it begins at the non-reducing ends! That was the point! And it must make a distinction because in the second paper I cited, it has a recognition site for a non-reducing end. The reducing end is topologically different.