We want to conjugate 10 mg of each of 2 proteins (lyophilized). One is 14 kDa and the other is 44 kDa.

You should obtain the larger Zeba columns from Pierce, if you want to perform a larger scale reaction. We would suggest performing the conjugation on a much smaller scale. Not more than 100 µg of protein. In that case, the smaller desalting columns would be sufficiently large. On the bottom of page 7 of the Protein-Protein conjugation kit manual, you are directed to add a large amount of HyNic in DMF because the amount of protein is large. Would suggest making 5 mg/mL stock solutions. You should scale this reaction down significantly, modifying just 100 µg of each protein. Would suggest modifying the larger protein with 15 equivalents of HyNic and the smaller protein with 5 equivalents of 4FB. 4FB is a much more efficient crosslinker.