Studies on bone enzymes. The assay of acid hydrolases and other enzymes in bone tissue

Unsuitability of indoxyl acetate as a substrate for the assay of testicular hyaluronidase

The most recently published method for the assay of testicular hyaluronidase preparations was based on the premise that the enzyme also exhibited carboxylesterase activity towards indoxyl acetate. Studies on the relative enzyme activities of various hyaluronidase preparations towards hyaluronate and indoxyl acetate, the relative stabilities towards pH, temperature and mechanical shaking and the behaviour towards a variety of inhibitors, showed that the activities towards the two substrates reflected the presence of at least two different enzyme systems in the preparations. Gel chromatography and polyacrylamide-gel-electrophoresis experiments confirmed these conclusions and the collective findings clearly establish that methods based on the use of indoxyl acetate cannot be employed to measure testicular hyaluronidase activity.

A new method for the preparation of rat liver lysosomes. Separation of cell organelles of rat liver by carrier-free continuous electrophoresis

A combination of differential centrifugation and carrier-free continuous electrophoresis is introduced as a new method for the isolation of animal cell organelles. Various buffers were systematically checked in order to find the system which preserves the organelles and gives as well a good separation in the free-flow electrophoresis apparatus. Triethanolamine-acetate buffer (10 mM), pH 7.4 was used. The isolated lysosomes were pure according to marker enzymes and electron micrographs. A heterogeneity of the lysosomes in electrophoretic mobility was demonstrated with respect to the marker enzymes arylsulfatase and beta-glucuronidase. The lysosomes with higher mobility showed a maximum enrichment of 240-fold with respect to arylsulfatase. The lysosomes with lower electrophoretic mobility showed a 65-fold enrichment with respect to beta-glucuronidase. The ratio of beta-glucuronidase to arylsulfatase varied from 2:1 to 1:2 in lysosomes of different mobility. The yield amounted to approximately 1 mg of lysosomal protein per gram of liver protein. 5-8 mg of lysosomes can be obtained in one experiment. The electrophoretic separation proves to be an effective tool in obtaining pure and well preserved lysosomes.

The locations of cathepsin activity and beta-glucuronidase in the Guerin T8 tumour

Tumour homogenate fractions, isolated by differential centrifugation, were subfractionated by density-gradient centrifugation. Biochemical and electron microscopic analyses revealed that beta-glucuronidase and cathepsin activity were associated with a class (possibly two) of lysosomal particles of density greater than those of mitochondria and the endoplasmic reticulum. Lysosomes sedimented by low g forces were vacuolar, electron-dense, delineated by a unit membrane and about 0.2mum in diameter. beta-Glucuronidase was also apparently associated with ribosomes whereas cathepsin was bound in part to the endoplasmic reticulum. Catalase and glucose 6-phosphatase possessed slightly different density-gradient sedimentation profiles.

On the mechanisms of bone resorption. The action of parathyroid hormone on the excretion and synthesis of lysosomal enzymes and on the extracellular release of acid by bone cells

Bone resorption, characterized by the solubilization of both the mineral and the organic components of the osseous matrix, was obtained in tissue culture under the action of parathyroid hormone (PTH). It was accompanied by the excretion of six lysosomal acid hydrolases, which was in good correlation with the progress of the resorption evaluated by the release of phosphate, calcium 45 or hydroxyproline from the explants; there was no increased excretion of two nonlysosomal enzymes, alkaline phosphatase, and catalase. Balance studies and experiments with inhibitors of protein synthesis indicated that the intracellular stores of the acid hydrolases excreted were maintained by new synthesis. The release was not due to a direct disruption of the lysosomal membrane by PTH; it is presumed to result from an exocytosis of the whole lysosomal content and to involve mechanisms similar to those controlling the secretion of this content into digestive vacuoles. The resorbing explants acidified their culture fluids at a faster rate and released more lactate and citrate than the controls; this release was in good correlation, in the PTH-treated cultures, with the resorption of the bone mineral, but the amount of citrate released was considerably smaller than that of lactate. The acid released could account for the resorption of the mineral. It is proposed, as a working hypothesis, that the acid hydrolases of the lysosomes are active in the resorption of the organic matrix of bone and that acid, originating possibly from the stimulation of glycolysis, cares for the concomitant solubilization of bone mineral while also favoring the hydrolytic action of the lysosomal enzymes.

Canine submandibular-gland hyaluronidase. Identification and subcellular distribution

1. Submandibular glands from four species of mammal have been shown to contain a hyaluronidase active at acid pH; glands from dog and cat had a much higher content of this enzyme than has been found in other sources. 2. Product formation from hyaluronate after 24hr. incubation was almost the same as with testicular hyaluronidase, indicating that the enzyme is an endo-poly-beta-hexosaminidase. 3. When submandibular-gland homogenates were fractionated by the scheme developed for liver by de Duve, Pressman, Gianetto, Wattiaux & Appelmans (1955), all the enzymes assayed, except cytochrome c oxidase, were found to occur partly in the soluble fraction and partly in the particulate fractions. Among the particular fractions, the highest specific activity was found in the heavy-mitochondrial fraction for cytochrome c oxidase, in the microsomal fraction for alkaline phosphatase and in the light-mitochondrial fraction for acid phosphatase, beta-N-acetylhexosaminidase and acid-active hyaluronidase. 4. Release of the enzyme activity from the sedimentable fractions occurred in 0.1% Triton X-100 or after high-speed homogenization. 5. Stimulation of dogs by pilocarpine was found to decrease the hyaluronidase content of the submandibular gland by 5% and to cause the occurrence of a corresponding amount of acid-active hyaluronidase in the submandibular saliva. 6. The results are discussed in relation to the subcellular localization of hyaluronidase.

Canine submandibular-gland hyaluronidase. Purification and properties

1. Methods for the purification of dog submandibular-gland hyaluronidase from sedimentable and non-sedimentable portions of a homogenate and from the whole homogenate are presented. The method consists of three main steps: removal of mucin by acid precipitation or gel filtration on Sephadex G-200, ammonium sulphate precipitation and CM-cellulose chromatography. By this method specific activities of up to 1.28 and 0.78mumoles of N-acetylglucosamine/min./mg. of protein were obtained for the purified freeze-dried non-sedimentable hyaluronidase and for the sedimentable hyaluronidase respectively. 2. A comparison of some of the properties of the non-sedimentable and the sedimentable hyaluronidase preparation indicated that there was little difference between the two and that they both resembled lysosomal hyaluronidase from rat liver.

Hyaluronidase activity in lysosomes of bone tissue

1. The distribution pattern of hyaluronidase in subcellular fractions of bone-tissue homogenates is closely similar to that reported by Vaes & Jacques (1965b) for the other acid hydrolases of this tissue. The highest specific activity of hyaluronidase is also found in the light-mitochondrial fraction. 2. In cytoplasmic extracts of bone, about 60% of the activity of hyaluronidase is latent, and is unmasked by a number of treatments (digitonin, low osmotic pressure, freezing and thawing, Waring Blendor) that unmask the lysosomal beta-glucuronidase in a closely parallel manner. Low concentrations of Triton X-100 render a larger proportion of beta-glucuronidase than of hyaluronidase accessible to external substrates, but release the same proportion of both enzymes in unsedimentable form. 3. These results support the concept of an association of hyaluronidase with lysosomes in bone.

Lysosomal hydrolases in calf thyroid

1. Two acid phosphatases (beta-glycerophosphatase and phenylphosphatase), acid beta-glucuronidase and cathepsin were demonstrated in the 0.25m-sucrose homogenates from whole calf thyroid tissue and from isolated calf thyroid cells. 2. The main kinetic characters of these enzymes were studied. 3. All these acid hydrolases are partially sedimentable and display a latency that is unmasked by treatment with Triton X-100 and on dilution in hypo-osmotic media. It is concluded that these acid hydrolases belong to the lysosomes.