Many polypeptide chains do not acquire enzymatic activity until they aggregate into a multimeric protein molecule. In these cases, the "active site" must spread over more than one chain, or, as we now guess more likely, aggregation causes conformational changes leading to enzymatic activity. Among these proteins is the bacterial enzyme β-galactosidase, whose smallest active form sediments at 16S and has a molecular weight generally thought to be about 500,000. Its subunit construction is clearly shown by its disaggregation into 4 subunits by 8 M urea (Zipser, 1963). Each of these urea subunits may have several polypeptide chains.
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Zipser et al. (1963) studied this question.