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The information on the initial step of enzymatic reaction of 2.5S RNA isolated from muscle 1,4-alpha-glucane branching enzyme (EC 2.4.1.18), isomerase amylose, has been reported for the first time. The 2.5S RNA-polysaccharide (starch) complex was isolated and partly characterized. It was shown that the complex retains its integrity during precipitation with ethanol, gel-filtration on a Biogel P-150 column and electrophoresis but dissociates into RNA and starch upon fractionation on a DEAE-52 cellulose column. Treatment of the original preparation with RNAase fully reflects the complex formation: with a decrease in the RNA content in the original preparation that of the synthesized complex diminishes. The RNA-polysaccharide complex exhibits the properties of the branching enzyme; its enzymatic activity markedly exceeds that of the free RNA.

Serine proteinase and metalloproteinase of Asp. oryzae, extracellular metalloproteinase of L. pneumophila and chymotrypsin-like proteinase of S. rutgersensis can hydrolyze pepsinogen by converting it into pepsin (pH 5.0, 37 degrees C). The localization of the site of hydrolysis depends on the nature of the enzyme: serine proteinase from Asp. oryzae induces the synthesis of a mixture of 60% pepsin, 25% leucyl-pepsin and 15% alanyl-leucyl-pepsin; metalloproteinase of Asp. oryzae converts pepsinogen only into leucyl-pepsin, while metalloproteinase of L. pneumophila yields a mixture of 33% pepsin, 53% leucyl-pepsin and 14% alanyl-leucyl-pepsin. Thus, the region of the activating pepsinogen peptide--Ala 42P-Ile 1 bond--seems to the most probable site for hydrolysis by exogenous proteinases. This site contains a Leu 44P-Ile 1 bond which is subjected to intermolecular hydrolysis during autocatalytic activation of pepsinogen. The experimental results emphasize the importance of the intermolecular pathway of pepsinogen activation.