Secretion of alpha-L-fucosidase by human embryonal skin fibroblasts

The amount of alpha-L-fucosidase secreted by normal human fibroblasts was higher in the medium containing 10% bovine serum than in the medium containing 0.1% bovine serum. Glycosidase secretion was twice higher at the advanced than at the initial stage of subcultivation. Extracellular activity of alpha-L-fucosidase from 3 different fibroblast strains differed insignificantly in the medium containing 0.1% bovine serum, while intracellular activity of the enzyme in these strains was altogether different. The results suggest that the lysosomal glycosidase secretion is determined by the level of cellular endocytosis.     

Change in localization of cellular vesicular apparatus during differentiation of myoblasts into myotubules in cell culture

The study of changes in the intracellular processes during differentiation of myoblasts into myotubules is of great importance for understanding several fundamental problems of cell biology. At first, this concerns the spatial organization of vacuolar apparatus that reflects the alterations in the properties of cell membranes, cytoskeleton elements and dynamics of vesicular transport in the course of differentiation. The distribution of acidic membrane organelles (lysosomes, late endosomes, Golgi cisternae) during the myotubule formation was revealed. It was shown that perinuclear localization of acidic organelles in myoblasts was replaced by diffuse distribution of these structures in the whole volume of myotubules. Using lipophilic fluorescent dyes, RH 414 and di-8-ANEPPS, the process of formation and dynamics of endocytic vesicles in myoblasts and myotubules was investigated. In the present work, semiconductive nanocrystals, quantum dots (QDs), conjugated with TAT-peptide, which belongs to cell-penetrating peptides, were used to characterize nonspecific endocytosis. It was shown that QDs--TAT complexes penetrate myoblasts but do not penetrate myotubules even after 24 h incubation, which might be connected with plasma membrane changes during the process of skeletal muscle differentiation.     

Inhibition of the activity of membrane-bound Ca2+-ATPase in the sarcoplasmic reticulum fragments of rabbit skeletal muscles by the alkaloid sanguinarine

Sanguinarine, a plant DNA-intercalator, is shown to inhibit the enzyme activity of the membrane-bound Ca2+-ATPase of rabbit skeletal muscle sarcoplasmic reticulum fragments. This inhibition could be interpreted by the well known ability of this alkaloid to interact with sulphydryl groups of the enzymes. Sanguinarine is a weaker inhibitor of this reaction than a sulphydryl group poison Ag+. The I50 is 3.10(-6) M for Ag+ and 7.10(-5) M for sanguinarine in the reaction medium with NO3- substituted for Cl-. In the standard reaction medium containing Cl-, the I50 for sanguinarine is 1.8.10(-4) M. In this case sanguinarine activates Ca2+-ATPase at low concentrations presumably because of uncoupling ATP hydrolysis from Ca2+ transport through membrane. Other agents studied are: DNA-intercalators--ethidium bromide, acriflavine, acridine orange; DNA-complexing antibiotics--actinomycin D, and olivomycin, alkaloids, quinine, morphine, berberine and an uncoupler of oxidative phosphorylation 2,4-dinitrophenol. These were found not to inhibit Ca2+-ATPase activity up to the concentrations of 10(-3)-10(-4) M.     

Relation between Mg2+ activation and AMP inhibition of fructose-1,6-diphosphatase from rabbit skeletal muscles

It was shown that AMP, an allosteric inhibitor of fructose-1.6-bisphosphatase, decreases the apparent affinity of the enzyme for the activating cation, Mg2+, which is accompanied by a decrease of the kinetic cooperativity between the Mg2+-binding sites. In its turn, the Mg2+ increase diminishes the enzyme sensitivity to the inhibiting effect of AMP and decreases the cooperativity of the inhibitor binding. The heterotropic interactions between the allosteric inhibitor and activator binding centers are consistent with the predictions of the Monod-Wyman-Changeux model which involves two conformational states of the enzyme (of which one is catalytically inactive) differing in their affinity for the ligands. An increase in pH from 7.4 to 9.0 increases the enzyme affinity for Mg2+ and causes an equilibrium shift towards the catalytically active state of the enzyme.     

Investigation of the tissue growth processes in porous implant

Investigation of the cell (osteocytes, fibroblasts and keratinocytes) adhesion and penetration in pores of the titanium pylon in vivo on the laboratory animals (Wistar rats) has been performed. The titanium pylon has been implanted in bone of a rat's thigh residuum. Electronic scanning and morphological analysis demonstrated the certain integration of the pylon with the surrounding tissues. The latter opens a possibility for development of direct skeletal attachment of limb prostheses.     

Molecular weight and tertiary structure of transketolase from baker's yeast]

Molecular weight of native apotransketolase from baker's yeast is found to be 159000 +/- 6000 by means of sedimentation equilibrium and sedimentation-diffusion rate. The enzyme in a relatively low concentration reversibly dissociates into two subunits with molecular weight of about 80 000 at pH 7.6 and 20 degrees C. The equilibrium constant of the reaction monomer-dimer is 4.4 . 10(3) M-1. A decrease of the temperature stimulates the association of monomers into dimer, while the shift of pH 7.6 into acid or alkaline region stimulates the dissociation process. Dissociation becames irreversible at pH less than 5 and greater than 10.5.