Gliadens CAN be separated from Glutenins. One method is by ethanol.
Also, Gliadens are not a precursor to Glutenins. They are different types. Gliadens are momomers and are soluble in 50 % ethanol. Glutenins are polymers, are insoluble in ethanol and are of a high molecular weight.
In water, Gliadens present as a honey-like viscous fuid whereas glutenins are of a low extensibility, very strong and mainly elastic.
The
The mixture of the two is what about for visocelastic properties and extensibility of "gluten" with gliadens functioning mainly as a plasticizer for glutens depending on homogeneous mixing.
(paraphrased from source- The Role of Gluten Elasticity in the Baking Quality of Wheat, R. Kieffer, MühlenchemieThe Role of Gluten Elasticity in the Baking Quality of Wheat, R. Kieffer, Mühlenchemie - retrieved February 26, 2018)