Anti-Liver Arginase antibody [ARG1/1125] - BSA and Azide free (ab212522)

This data was produced with ab215843, the same antibody in a different formulation with BSA and Azide.
ab215843 was tested in protein array against over 19000 different full-length human proteins.
Z- and S- Score: The Z-score represents the strength of a signal that a monoclonal antibody (MAb) (in combination with a fluorescently-tagged anti-IgG secondary antibody) produces when binding to a particular protein on the HuProtTM array. Z-scores are described in units of standard deviations (SD's) above the mean value of all signals generated on that array. If targets on HuProtTM are arranged in descending order of the Z-score, the S-score is the difference (also in units of SD's) between the Z-score. S-score therefore represents the relative target specificity of a MAb to its intended target.
A MAb is specific to its intended target if the MAb has an S-score of at least 2.5. For example, if a MAb binds to protein X with a Z-score of 43 and to protein Y with a Z-score of 14, then the S-score for the binding of that MAb to protein X is equal to 29.

All lanes : Anti-Liver Arginase antibody [ARG1/1125] - BSA and Azide free (ab212522) at 0.5 µg/ml

Lane 1 : Recombinant Arginase protein fragment
Lane 2 : Human liver tissue lysate

Predicted band size: 35 kDa
Observed band size: 35-38 kDa why is the actual band size different from the predicted?