Understanding the Question:
The question asks how many amino acids make up the human H1 receptor protein.
Key Concept:
Each histamine receptor subtype (H1 through H4) is a distinct G-protein coupled receptor with its own fixed protein length, so this is a direct recall of the documented sequence size for H1 specifically.
Checking Each Option:
359 amino acids is closer to the reported length of the H4 receptor, a smaller subtype, not H1.
445 amino acids sits closer to the H2 receptor's reported length.
390 amino acids does not match any of the standard reported histamine receptor lengths for H1.
487 amino acids is the documented length of the human H1 receptor, the largest of the four histamine receptor subtypes.
Final Answer:
The human H1 receptor protein is made up of 487 amino acids.