Hyaluronidase has been investigated in various strains of pneumococci and hemolytic streptococci, and in some material of animal origin. The enzyme activity was measured by a viscosimetric method using as a substrate a fluid containing hyaluronic acid as the viscous component, and by the hydrolysis of pure hyaluronic acid into its reducing components.

In pneumococci the enzyme was demonstrated in all types and in all strains tested, including smooth and rough forms of Types I, II, III, and VI.

In hemolytic streptococci the enzyme from strain H44, group A, reported previously, was further investigated. In this strain, as well as in other hemolytic streptococci containing the enzyme, great variability of the enzyme concentration was found. Furthermore, the enzyme proved to be very labile, giving in the viscosimetric measurements a typical stoppage of the activity initially present. In 13 out of 14 other strains of group A organisms investigated, no enzyme was demonstrable, but the variation in activity in the enzyme-active strains renders the negative findings inconclusive. A very active enzyme, though of great variability, was found in one group C strain.

The enzyme was prepared from the leech in confirmation of the work of Claude.

The enzyme from testis showed a maximum at pH 4.4 in contrast to the optimum of 5.8 in pneumococcal, streptococcal, and Cl. welchii preparations. The pH curve of the testis enzyme indicated, however, a second optimum coinciding with that of the bacterial enzymes. The hydrolysis further indicated a break at about 50 per cent hydrolysis, indicating primarily the hydrolysis down to aldobionic acid units. The depolymerizing action of testis enzyme is more marked than that of pneumococcal enzyme. The results have been interpreted as due to the presence of two enzymes, one attacking the long chain molecule, the other hydrolyzing the aldobionic acid formed.

The enzyme was further prepared from beef spleen. Here the hydrolysis of ß-glucuronides was compared to that of hyaluronic acid. The two actions apparently are catalyzed by two distinct enzymes.

Enzyme preparations were further obtained from rabbit skin. Since hyaluronic acid has also been found in the skin, this organ may play a considerable rôle in the metabolism of hyaluronic acid.

In addition to hyaluronic acid, it has been shown that hyaluronidases also hydrolyze the sulfuric acid containing polysaccharide of the cornea. This polysaccharide has previously been characterized as a natural sulfuric acid ester of hyaluronic acid. The pneumococcal enzyme preparations also attacked a polysaccharide acid prepared from submaxillary gland, which is not hyaluronic acid. However, it is believed that this hydrolysis is due to a second enzyme contained in the preparations. The testis enzyme, on the other hand, attacked chondroitinsulfuric acid and also contained a sulfatase.

The depolymerizing action of hyaluronidase has been discussed. It is concluded that depolymerization and hydrolysis are probably due to the same enzyme attacking hyaluronic acid. It is suggested that the first attack of the enzyme does not cause an opening of glucosidic linkages. The available evidence indicates that the viscosity of the natural fluids is not due to macromolecules but to micellae formation, and that these micellae are depolymerized by the enzymatic reaction. It is assumed that the depolymerization is due to a primary enzyme-substrate reaction, which in itself is insufficient to open the glucosidic linkages. The latter reaction involves further steps.

The relationship between hyaluronidase and "spreading factor" has been discussed anew. Though more data have been reported pointing to the identity of hyaluronidase and "spreading factor," our inability to demonstrate hyaluronidase in streptococcal material of high "spreading" potency, is still a serious obstacle to the unitarian theory. However, it seems possible that the streptococcal material may contain reversibly inactive enzyme which may be reactivated in vivo.

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