[Changes in the activity of lactate dehydrogenase isoformes in mouse rhabdomyosarcoma under different proliferation conditions]. / Izmenenie aktivnosti izoform laktatdegidrogenazy v rabdomiosarkome myshi pri raznykh usloviiakh proliferatsii.

The activity of lactate dehydrogenase (LDH) isoenzymes was studied in clones of rhabdomyosarcoma (RMS) MX-53, being transplanted on mice of CC57W line. Clones obtained in lungs after the intravenous injection of a tumor cell suspension were transplanted into subcutaneous connective tissue (SCT) and eye anterior chamber (EAC). A study of LDH isoenzymes spectrum in transplants and native muscle tissues has been made using polyacrylamide gel electrophoresis and densitometry. We revealed a variability of LDH isoenzyme activity within one clone, and in population of clones under different proliferation conditions. Under all the proliferation conditions, we observed spectra characteristic of tumors of a given histogenesis with predominating activity of M-subunits. But during proliferation in EAC the M:H ratio decreased, and LDH spectra of tumor cells became more similar to the LDH spectrum of normal skeletal muscles. It is concluded that intra- and interclonal variations of the character "LDH isozyme spectrum" is strongly influenced by the environmental factors.

[Enzymatic hydrolysis and reversible binding of suberyldicholine by cholinesterases]. / Fermentativnyi gidroliz i obratnoe sviazyvanie suberildikholina kholinesterazami

A hydrolysis of suberyldicholine and monocholic ester of suberic acid by butyrylcholinesterase was studied. In the region of Sopt the rates of suberyldicholine hydrolysis were slightly below and under S less than Sopt they were far in excess of the rates of acetylcholine hydrolysis. The following kinetic constants of hydrolysis were obtained: for suberyldicholine--Km=2.3-10(-5)M, V=2.4 mcM/mg. min, Kss=7.2-10(-2)M; for monocholic ester of suberic acid--Km=7.5-10(-4)M, V=1.5 mcM/mg, min, Kss=1.2-10(-2)M (25 degrees, pH 7.5, 0.1 M KCl). Suberyldicholine was shown to be highly active reversible inhibitor of competitive--non-competitive type (Ki=2.3-10(-6)M, alpha=0.5) of acetylcholinesterase from human erythrocytes; the inhibitory effect of monocholic ester of suberic acid was distinctly lower. By biological and indirect biochemical methods it was found that low concentrations of suberyldicholine 10(-5)=10(-6)M (similar to concentrations that were in an organism upon myorelaxation) were hydrolyzed by acetlycholinesterase with the rate, approximately equal to the rate of acetylcholine hydrolysis. The reversible binding and the enzymatic hydrolysis of suberyldicholine by acetylcholinesterase of tissues were likely to be the main factors that determined the effectiveness and prolonged blocking action of suberyldicholine on the nerve-muscle conductivity.

[Effect of cholinesterase inhibitors and reactivators on the blocking action of dicarboxylic acid amino esters on neuromuscular conduction]. / Vliianie ingibitorov i reaktivatorov kholinésteraz na blokiruiushchee deístvie aminoéfirov dikarbonovykh kislot na nervno-myshechnoe provedenie

Inhibition of active cholinesterases in cats with armine or the GT-165 compound (0,0-diethyl-S-/beta-arylmethylamino) ethyl/thiophosphate methylsulphomethylate) potentiases ten- and hundred-fold the blocking action of subecholine and its derivatives on the neuro-muscular condution. The cholinesterase reactivator dipyroxime (2-5 mg/kg) quickly lifts the conduction block, provoked by muscle relaxants of the subecholine type under the cholinesterase inhibition. The subecholine analogue with a single propyl radical at each atom of nitrogen does not display any pressor action and, upon inhibition of cholinesterases, it blocks the neuro-muscular conduction when used in a dose of 0.1-0.2 gamma/kg. The maximal potentiation of the blocking action exerted by subecholine and its analogues is achieved in inhibiting not only pseudocholinesterase but acetylcholinesterase as well.