Complete hydrolysis of polypeptides with insolubilized enzymes

Automated protein hydrolysis delivering sample to a solid acid catalyst for amino acid analysis

In this study, we developed an automatic protein hydrolysis system using strong cation-exchange resins as solid acid catalysts. Examining several kinds of inorganic solid acids and cation-exchange resins, we found that a few cation-exchange resins worked as acid catalysts for protein hydrolysis when heated in the presence of water. The most efficient resin yielded amounts of amino acids that were over 70% of those recovered after conventional hydrolysis with hydrochloric acid and resulted in amino acid compositions matching the theoretical values. The solid-acid hydrolysis was automated by packing the resin into columns, combining the columns with a high-performance liquid chromatography system, and heating them. The amino acids that constitute a protein can thereby be determined, minimizing contamination from the environment.

Nerve injury stimulates the secretion of apolipoprotein E by nonneuronal cells

Nerve trauma initiates significant changes in the composition of proteins secreted by nonneuronal cells. The most prominent of these proteins is a 37-kDa protein, whose expression correlates with the time course of nerve development, degeneration, and regeneration. We now report that the 37-kDa protein is apolipoprotein E (apoE). We produced a specific antiserum against the 37-kDa protein isolated from previously crushed nerves. This antiserum recognizes a 36-kDa protein in rat serum that we have purified and identified as apoE. The anti-37-kDa antiserum also recognizes apoE on electrophoretic transfer blots of authentic samples of high and very low density lipoproteins. The nerve 37-kDa protein comigrates with apoE by two-dimensional electrophoresis, shares a similar amino acid composition, and reacts with an antiserum against authentic apoE. The purified apoE specifically blocks the immunoprecipitation of [35S]methionine-labeled 37-kDa protein synthesized by nonneuronal cells. Thus, on the basis of its molecular mass, isoelectric point, amino acid composition, and immunological properties, we conclude that the 37-kDa protein is apoE. We also used light microscopic immunohistochemistry to localize apoE following nerve injury. In rats with optic nerve lesions, the 37-kDa antiserum bound specifically to the degenerating optic tracts and to the retino-recipient layers of the lateral geniculate nucleus and the superior colliculus. We propose that apoE is synthesized by phagocytic cells in response to nerve injury for the purpose of mobilizing lipids produced as a consequence of axon degeneration.

Cyanogen-induced gamma-glutamyl to imidazole cross-link in carbonic anhydrase. A unique mode of inhibition

The irreversible inhibition of carbonic anhydrase by cyanogen occurs by a unique mechanism. Cyanogen is an affinity label: it behaves like a carbodiimide and produces an intra-molecular cross-link without being incorporated. The nucleophile-labile cross-link is formed between a gamma-COOH of a Glu and an imidazole of a His with a 1:1:1 stoichiometry with the enzyme. The deletion of approximately 1 Glu and approximately 1 His was noted by amino acid analysis of enzymatically hydrolyzed carbonic anhydrase. The modified Glu was converted to 2,4-diaminobutanoic acid and quantitated by amino acid analysis. The presence and quantity of modified His was supported through high-resolution proton NMR analysis.