Lenin

It's more a measure of the amino acid constituents.
Animal proteins are made of an amino acid composition that is similar to what we need...being animals.
Vegetable proteins are not balanced well for humans but they can be combined to complement the weaknesses of one vegetable with the strengths of another.
For example neither rice nor bean protein is particularly "useable" but rice and beans TOGETHER will easily support life with a much more nearly balanced and "useable" composition of amino acids.

Same with wheat and legumes.

Probably the most useable proteins are those in egg and milk, because both are geared to provide a perfect balance to totally support growth with no other protein source.

THe usual standard is to measure the NPU (net protein utilization which pretty much runs from near 100(%) for completely useable to the low 30's for some grains and down near 0% fpr some one ot two amino acid proteins like gelatin.

Of course, any protein in excess of what the body needs is either burned or converted to fat no matter HOW "useable" it is.

Some new research is showing that this "balancing" is not as important as previously thought.

Proteiun supplements on the market today have a very high NPU whether soy or whey or casein based. Soy is the most balanced and useable protein in the vegetable world.

I looked for a good list online but there is too much clutter from health food stores sellingg stuff. Maybe you can be more persistent than I.