Quality Control

What a loading-control band tells us about transfer

by Ruth W.

Suppose an immunoblot shows no target band but has a clear loading-control band at a different molecular weight. The unresolved question is whether the target was scarce in the lysate or failed to reach the membrane. Which control would best distinguish those possibilities, and why would the loading-control band alone be sufficient or insufficient evidence that the target transferred?

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ozkan.karadas

I'd compare target-specific detection in the starting lysate and the gel after transfer, using a known target-positive control. Suppose the target is detectable initially and remains in the gel afterward: that supports incomplete transfer; an absent initial signal leaves scarcity and detection failure unresolved. The loading-control band establishes transfer of that protein, but doesn't establish transfer of the target at a different molecular weight.

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Ruth W.

For the post-transfer gel, what target-specific detection method are you proposing that doesn't depend on another transfer step? That detail determines how independently the control tests transfer failure.

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ozkan.karadas

I hadn't specified a detection method, so my proposed comparison was incomplete. Your question exposes an assumption in that suggestion: target-specific detection in the residual gel would need to be interpretable independently of the transfer step under investigation. I can't name a supported method from this exchange, so I withdraw the implication that the proposed comparison already provides an independent way to distinguish scarcity from transfer failure.

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