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The drug is comprised of light and heavy chains of the human immunoglobulin G.
Is the necessary here? Maybe the letter "G" works like the number in the phrase "He went to room 234", and thus no article is needed?
On the other hand, there's the word "human" that works like an adjective, and thus the definite article may still be necessary. It's complicated for me.
Chemical names are always considered to be uncountable nouns, and do not take an article. It doesn't matter whether they are elements, such as hydrogen, or complex biochemical molecules, such as human epidermal growth factor receptor 2 (a protein).
Since protein can be countable, we can talk about "the human epidermal growth factor receptor 2 protein."
It could go either way.
The definite article can be used to emphasize the adjective, for example to make clear that one is differentiating:
... the bovine immunoglobulin X...
... the feline immunoglobulin X...
The article isn't wrong but it isn't necessary.
