Subunit Dissociation and Unfolding

Alanine racemase of B. stearothermophilus consists of two identical subunits, whereas both DadB and air enzymes of Salmonella typhimurium and the Streptococcusfaecalis enzyme occur in a form of monomer. Toyama et al.14) examined whether the monomeric form of the B. stearothermophilus enzyme is catalytically active. They studied the guanidine HC1-induced subunit dissociation and unfolding of the enzyme by fluorescence and absorption spectroscopies, circular dichroism (CD) analysis, and gel filtration.I4) The overall process was found to be reversible more than 75% of the original activity was recovered by decreasing the denaturant concentration. 

The enzyme was unfolded by guanidine HC1 treatment through two detectable phases Phases 1 and 2 were observed by fluorescence spectroscopy derived from tryptophan residue.14 The fluorescence maximum moved gradually from 336 to 331 nm as the 

The subunit dissociation is usually accompanied by destruction of the secondary structures when thermolabile proteins are used. The thermostable alanine racemase is very useful for studying the mechanism of subunit dissociation and protein unfolding. 

---