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虫号: 1053480
注册: 2010-07-07
专业: 膜生物化学与膜生物物理学

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Kallikreins I-IV each gave two protein bands, H and L, on SDS-polyacrylamide gel electrophoresis after reductive cleavage of disulfide bonds. By analyzing electrophoretically the H and L bands from each of the kallikreins, we found that kallikreins I—IV can be expressed as H1L1, H1L2,H2L1 and H2L2, respectively. H1 and L1 contained carbohydrate, and all the available findings supported the idea that H2, and L2 corresponded to carbohydrate-free forms of H1 and L1, respectively. The differences in the apparent molecular weights between H1 and H2, and between L1 and L2 , determined by SDS-polyacrylamide gel electrophoresis at various gel concentrations, did not necessarily correspond to the size of the carbohydrate moieties. This is due to the fact that there is no theoretical basis for determining the molecular weight of proteins (such as glycoproteins) which show anomalous Ferguson plots.
The subunit structures and carbohydrate compositions of various kallikrein preparations so far reported are confusing, probably due to insufficient purity of the preparations. The recent report of Fiedler and Hirschman (7) is the only one which pointed out the presence of four forms of kallikrein. Although no systematic procedures to prepare these four forms have been described, the subunit structures and amino acid compositions of these four forms are very similar to those we found. However, no conclusive data was presented as regards the molecular weight and carbohydrate composition of each subunit.
Considering the carbohydrate contents of kallikreins I—III, some microheterogeneities, especially those with respect to sialic acid, are apparent. It is unclear if this heterogeneity was produced during the autolysis. However, the heterogeneities seen in the composition did not result in multiple peaks in electrophoresis nor in isoelectric focusing. This is in contrast to previous observations that various kallikrein preparations gave multiple peaks on isoelectric focusing (5, 6, 23, 24).

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