Final answer:
Option B (FLGFQY) is most likely to produce results similar to SP1.7 because it retains the crucial C-terminal phenylalanine and introduces a tolerated glutamine residue in place of histidine.
Step-by-step explanation:
The question revolves around substituting the bioactive heptapeptide SP1.7 with a peptide that would most likely achieve the same experimental results. Given your options of different peptides (A-D), we must consider what modifications to H-Phe-Phe-NH₂ would retain binding affinity and improve pharmacokinetic properties while also being resistant to metabolic degradation and efflux.
Based on the information provided, which emphasizes the importance of the C-terminal phenylalanine and the potential for N-terminal modifications, option B (FLGFQY) introduces a glutamine residue in place of histidine. This switch is tolerated in similar sequences without significant loss in affinity, and the other positions remain unchanged; thus FLGFQY is most likely to produce comparable results.