Yeast glycogen synthetase (uridine diphosphate glucose : glycogen α-4-glucosyltransferase) is inhibited at neutral pH by rather high concentrations of several anions, and addition of glucose 6-phosphate reverses this effect. It has now been found that many substances are much more effective inhibitors at pH 6, the reported value for the yeast cell, than at pH 7.5. At the acidic pH, 5 mM adenosine triphosphate, adenosine diphosphate, or guanosine triphosphate inhibits the enzyme about 90%. Glucose 6-phosphate acts as reactivator in this case too. By several criteria these nucleotides are shown to act as allosteric inhibitors. A possible mechanism of regulation of glycogen synthesis is proposed, according to which the combined concentrations of adenosine triphosphate plus adenosine diphosphate would always be sufficient for almost complete inhibition of the enzyme in the absence of glucose 6-phosphate. The concentration of phosphoric ester would then determine the activity of the enzyme. At high adenosine triphosphate: adenosine monophosphate ratios, phosphofructokinase would be inhibited and glucose 6-phosphate would accumulate, thus relieving the inhibition of glycogen synthesis. The opposite effect would take place at low adenosine triphosphate:adenosine monophosphate ratios. Ammonium ion, when present, would also act on the phosphofructokinase reaction, helping to channel the carbon of glucose toward the formation of amino acids and other nitrogenous substances.
Documento: | Artículo |
Título: | Allosteric properties of yeast glycogen synthetase. II. The effect of pH on inhibition and its physiological implications |
Autor: | Rothman, L.B.; Cabib, E. |
Filiación: | Instituto de Investigaciones Bioquímicas Fundación Campomar, Facultad de Ciencias Exactas y Naturales, Obligado 2490, Buenos Aires (28), Argentina Consejo Nacional de Investigaciones Científicas y Técnicas |
Idioma: | Inglés |
Año: | 1967 |
Volumen: | 6 |
Número: | 7 |
Página de inicio: | 2107 |
Página de fin: | 2112 |
Título revista: | Biochemistry |
ISSN: | 00062960 |
Registro: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00062960_v6_n7_p2107_Rothman |