Interaction of muscle glycogen phosphorylase b reconstituted from apoenzyme and analogs of pyridoxal-5'-phosphate with specific ligands.

Phosphorylase b from rabbit skeletal muscles was reconstituted with analogs of PLP containing residues -CH(2)-CH(2)-COOH, trans-CH=CH-COOH or -C=-COOH at position 5. Replacing native coenzyme in the phosphorylase molecule with any PLP analog tested leads to the decrease in the enzyme affinity for the allosteric inhibitor, FMN. Phosphorylase b reconstituted with analogs of PLP shows the greater ability for association in tetramers in the presence of 1 mM AMP than native enzyme.

[Reconstruction of muscle glycogen phosphorylase b from an apoenzyme and pyridoxal-5'-phosphate and its analogs. Interaction of apophosphorylase and the reconstructed enzyme with specific ligands]. / Rekonstruktsiia myshechnoi glikogenfosforilazy b iz apofermenta i piridoksal'-5'-fosfata i ego analogov. Vzaimodeistvie apofosforilazy i rekonstruirovannogo fermenta so spetsificheskimi ligandami.

Sedimentation methods were used to study the effects of modification of the pyridoxal-5'-phosphate (PLP) molecule at the 5th position on the affinity of reconstituted muscle glycogen phosphorylase b for the substrate (glycogen) and the allosteric inhibitor (FMN) as well as on the enzyme capacity to association induced by AMP. Reconstituted phosphorylase b was obtained with PLP analogs containing at the 5th position -CH2-CH2-COOH (analog I), trans-CH=CH-COOH (analog II) or -C identical to COOH (analog III) residues. Reconstitution of phosphorylase b is accompanied by the recovery of the enzyme quaternary structure. Phosphorylase b reconstituted with PLP or analogs I, II and III is not distinguished practically from the native enzyme in its affinity for glycogen. Substitution of the native coenzyme in the phosphorylase molecule with any tested PLP analog leads to lower enzyme affinity for FMN. Microscopic dissociation constants of the FMN-enzyme complexes increase in the following order: enzyme.I < enzyme.II < enzyme.III. Phosphorylase b reconstituted with analogs I, II and III differs substantially from the native enzyme in its capacity to association in the presence of 1 mM AMP: the reconstituted enzyme is represented practically by only the tetrameric form.

[Analogs of 3'-dephospho-CoASH with a phosphodiester bond as substrates of the S-acetylation reaction, catalyzed by acetyl-CoA-synthetase fom rabbit myocardium]. / Analogi 3'-defosfo-CoASH s fosfodiéfirnoi sviaz'iu kak substraty reaktsii S-atsetilirovaniia, kataliziruemoi atsetil-CoA-sintetazoi miokarda krolika.

A number of earlier unknown 3'-dephospho-CoASH analogues with the pyrophosphate fragment replaced by an ester or phosphodiester bond were synthesized and tested in S-acetylation reaction, catalyzed by acetyl-CoA synthetase (EC 6.2.1.1) from rabbit myocardium. 3'-Dephospho-CoASH analogues with a phosphodiester bond, e.g. (Ia), had a lower affinity and diminished kinetic parameters than 3'-dephospho-CoASH (Km = 1 and 0.2 mM, respectively). The adenine substitution in (Ia) by guanine or hypoxanthine (but not cytosine) residue resulted in a loss of substrate properties. 3'-Dephospho-CoASH with an ester bond were not capable of accepting acetate under conditions used and only slightly inhibited the enzymic activity.

[Substrate specificity of acetyl-CoA-carboxylase from the rat liver]. / Izuchenie substratnoi spetsifichnosti atsetil-CoA-karboksilazy pecheni krysy.

The interaction between acetyl-CoA fragments and rat liver acetyl-CoA carboxylase was studied. It was found that the 3'-phosphate group did not interfere with the enzyme interaction since the substrate properties of acetyl-dephospho-CoA and acetyl-CoA are nearly identical. The non-nucleotide substrate analogs S-acetyl-pantethin and its 4'-phosphate) also displayed substrate properties (V = 1.5% and 15% of the V for acetyl-CoA carboxylation respectively). The nucleotide fragment of the acetyl-CoA molecule produced an appreciable effect on the thermodynamics of this substrate interaction with the enzyme. Its physiological role consists in all probability, in the activation and propes orientation of the acetyl group in the enzyme active center. The far more pronounced substrate properties of S-acetyl pantethin 4'-phosphate and the inhibitory properties of pantethin 4'-phosphate (compared to non-phosphorylated analogs) suggest the essential role of the beta-phosphate residue of ADP in the acetyl-CoA binding to the enzyme. The data obtained suggest also that the hydrophobic region responsible for the acyl radical binding, has a site which specifically recognizes the beta-mercaptoethyl residue of the CoA pantethin fragment. The pivotal role in the acetyl-CoA carboxylase interaction with the substrate is ascribed to the productive binding of the acetyl radical; the contribution of individual fragment of the CoA molecule is variable.

[Antihypoxic properties of GABA-containing vitamin derivatives]. / Antigipoksicheskie svoistva GAMK-soderzhashchikh proizvodnykh vitaminov.

The antihypoxic properties of GABA-containing vitamin derivatives (pyridoxalphosphate-GABA, picamilone, pantogam, sodium homopantothenate) as compared with GABA were studied. All agents were found to increase mouse life expectancy under hypoxia in contrast to GABA.

[Interaction of muscle glycogen phosphorylase b with nicotinic acid, nicotinamide, N-nicotinyl-gamma-aminobutyric acid and nicotinamide coenzymes]. / Vzaimodeistvie myshechnoi glikogenfosforilazy b s nikotinovoi kislotoi, nikotinamidom, N-nikotinoil-gamma-aminomaslianoi kislotoi i nikotinamidnymi kofermentami.

The inhibitory action of nicotinic acid, nicotinamide, N-nicotinoyl-gamma-aminobutyric acid, NAD, NADH, NADP, and NADPH on the rabbit skeletal muscle glycogen phosphorylase b has been studied. The inhibition is reversible and positively cooperative (the value of Hill coefficients were determined for the following compounds: nicotinic acid (28 mM; 1.4), nicotinamide (4.4 mM; 1.2), N-nicotinoyl-gamma-aminobutyric acid (9.5 mM; 1.4), NAD (4.4 mM; 1.2), NADH (0.93 mM; 1.2). NADH-binding site of glycogen phosphorylase b subunit was characterized by the sedimentation velocity method. Microscopic dissociation constant was found to be 86 +/- 9 microM (pH 6.8; 20 degrees C). AMP-induced association of glycogen phosphorylase b is hindered by NADH.

[Signal trait of cucumbers]. / Signal'nyi priznak u ogurtsa.

A mutant of cucumber characterized by the absence of nappiness on all the organs of the plant was found at Birjuchekutian station in 1970. This character is recessive and is manifested in the second generation showing a 3:1 ratio of nappy and plain plants. On the basis of this mutant, forms of cucumber without nappiness were obtained. Plain plants are distinguished especially well at the initial stages of development when the first leaf appears. They are viable and productive, grow perfectly well and possess a high combining ability.