= Solution
The main particles are approximately \b[120 kDa in both conditions]. With 30 kDa per <protein> subunit, this supports a tetramer:
$$
\boxed{N\simeq\frac{120\,\mathrm{kDa}}{30\,\mathrm{kDa}}=4.}
$$
The small <peptide> contribution is not clearly resolved as a separate mass increase at this scale. Together with the microscopy, the results support a conformational change of an existing tetramer, rather than a large change in oligomer number. <Mass photometry> reports the scattering-derived mass distribution of detected particles; it does not by itself identify which conformation a particle adopts or count small bound <ligands> precisely.
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