Some detective work
When I started research work on Rhizobium, a major textbook showed the infection thread going through the plasma membrane (yes, a three-way biomembrane junction!) and then simply ending, cut off, (when have you seen a biomembrane end?) and emptying bacteria/bacteroids into the host cell.
Sorry for resorting to to sacasm, but a lot of other stuff was pretty naive too:
Slop your homogenate onto a step gradient and call everything between 1.2 and 1.25 g/ml "pure symbiosomes". Check purity with a light microscope so as not to see the other membrane debris, thus ensuring that PBM made from these symbiosomes is equally "pure"
Slop your homogenate onto a step gradient and call everything at 1.14 g/ml "pure plasma membrane", even when it's 1 or 2% of total cell protein. Don't bother checking any marker enzymes!
Don't assay plant ATPase at 22 degrees C, use 37 degrees instead, because it stimulates the pH6 activity 10-fold and drastically inhibits the pH8 acivity, thus providing much clearer results!
To be slightly more serious, there is apparently still some residual confusion about the molecular mass of Choline Kinase II, due to a rather aging report from Harwoods lab that assumed that the major band in an impure preparation was actually the enzyme. However click here for what Harwood actually found (PDF format).
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