Re: How did scientist test for the different membrane protiens?

I will assume that by peripheral and integral proteins, you are referring 
in both cases to membrane-associated proteins.  The definition is largely 
operational although we think we understand the physical basis.

Intregral membrane proteins are proteins that cannot be removed from a 
membrane and solubilized unless the membrane is literally dissolved with 
detergent, whereupon the membrane protein becomes "soluble" in the 
hydrophobic environment of the detergent.

Peripheral membrane proteins can be loosely or tightly associated with the 
membrane depending on their mode of attachment.  Since the surface of the 
membrane lipid bilayer is generally negative on the inside and slightly 
positive on the outside, proteins can bind electrostatically, that is by 
charges on the lipid and opposite charges on the protein.  This is the 
weakest form of association.  Such proteins can usually be removed by 
washing the membrane in a buffer with high salt (1.0M NaCl for example).  
Then proteins can have an amphipathic alpha-helix (one face of the helix 
hydrophobic, one side hydrophilic) that lies parallel to the membrane and 
partially imbedded into one-half of the lipid bilayer.  This is a stronger 
type of interaction, but can usually be removed by low concentrations of 
detergent without disrupting the bilayer.  Finally, proteins can be 
attached by various lipids, generally fatty acids, or glycolipids (fatty 
acids covalently bonded with a sugar polymer).  The fatty acid inserts 
into one-half of the bilayer and holds the protein to the membrane 
although the protein itself is not within the membrane.  This type of 
interaction can be detected by use of several types of enzymes which cut 
off the lipid or glycolipid thus solubilizing the protein.  Mild detergent 
will also remove such proteins sometimes.