The proflavin-induced increase in the catalytic activity of ficin

The specificity of actinidin and its relationship to the structure of the enzyme

The kinetic parameters kcat, Km and kcat/Km, have been determined for the actinidin-catalysed hydrolyses of N-substituted amino acid esters and amides and compared to the corresponding values for papain (EC 3.4.22.2). Substrates with aromatic N-substituents have lower kcat/Km values for actinidin (EC 3.4.22.14); the difference is much smaller for substrates with aliphatic substituents. The lower kcat/Km values for actinidin generally correspond to higher Km values suggesting that the strength of substrate binding differs between the two enzymes. This difference is explained in terms of the differences in the substrate binding sites found in X-ray crystallographic studies.

Fractionation of of proteolytic enzymes by affinity chromatography on sepharose aminocaproyl proflavin

The serine proteinases trypsin, chymotrypsin, elastase, and acrosin bind to the proflavin resin, the sulfhydryl proteinases ficin, bromelain, and papain are retarded by the resin, whereas most proteins and enzymes tested are not bound. Elution of the bound activities is accomplished NaCl or by variation from the pH optimum of the enzyme. Commercially available enzymes that are bound or retarded are easily further purified by the column. The acrosin activity of sperm acrosomal extracts is separated into bound and unbound activities. Acrosin is purified 120-fold from sperm acrosomal extracts in a single step, yielding a specific activity of 96.

On the prevalence of "nonspecific" binding at the specific binding sites of globular proteins

Strong binding of dyes to simple globular proteins takes place predominantly in areas overlapping the binding sites for substrates, coenzymes and prosthetic groups, in preference to other regions of the protein surface. The structure of the dyes bears no obvious relationship to that of the normal ligands. It is proposed that this phenomenon is a reflection of the special stereochemical features of such sites, their hydrophobicity relative to other portions of the protein surface, and, possibly, greater flexibility in these regions of the protein molecule. The binding properties of antibodies and bovine serum albumin are discussed in relation to this apparent versatility of protein binding sites towards structurally unrelated organic ligands.