Subunit Structure
The sedimentation constants and molecular weights of GI
vary from 7.55 to 11.45 and from 52,000 to 191,000, respectively (44). The subunit structure and amino acid composition
of GI reveal that it is a tetramer or a dimer of similar or
identical subunits associated with noncovalent bonds and is
devoid of interchain disulfide bonds. The extracellular GI from
Bacillus sp. is a trimer (42). Basuki et al. have reported the
existence of isozymes of GI from Streptomyces phaechromogenes
(14). The isoenzymes differ in their N-terminal amino
acids and in the peptide patterns of the digests with trypsin,
Achromobacter protease I, and cyanogen bromide. Each of the
isoenzymes was a tetramer of nonidentical subunits