Inhibition of liver fructose 1,6-bisphosphatase activity by Zn2+: reversal by imidazole pyruvate.

Imidazole pyruvate was found to be a very potent natural chelating agent in reversing the inhibition of liver fructose 1,6-bisphosphatase activity by Zn2+. This metabolite may play a physiological role in gluconeogenesis.     

Immobilization of chicken liver fructose 1,6-bisphosphatase on CNBr-activated Sepharose

Summary Chicken liver fructose 1,6-bisphosphatase is readily immobilized on CNBr-activated Sepharose. The immobilization alters some enzymatic properties. They include broader pH activity curve, loss of activation by K⁺ or NH ₄ ⁺ , increased resistance to inactivation by trypsin, decreased sensitivity to AMP inhibition, and loss of cooperative interaction among AMP-binding sites. The immobilized enzyme retains about 38% or 19% of the specific activity of the native enzyme when the activity is measured in the absence or presence of K⁺, resepctively.This work was supported by grant RR-8006 from the General Research Branch, Division of Research Resources, NIH (USA).     

Immobilization of chicken liver fructose 1,6-bisphosphatase on CNBr-activated Sepharose

Chicken liver fructose 1,6-bisphosphatase is readily immobilized on CNBr-activated Sepharose. The immobilization alters some enzymatic properties. They include broader pH activity curve, loss of activation by K+ or NH+4, increased resistance to inactivation by trypsin, decreased sensitivity to AMP inhibition, and loss of cooperative interaction among AMP-binding sites. The immobilized enzyme retains about 38% or 19% of the specific activity of the native enzyme when the activity is measured in the absence or presence of K+, respectively.     

Demonstration of fructose 1,6-bisphosphatase in human term placenta

Summary A proteolysed form of fructose 1,6-bisphosphatase (Fru-P₂ase) has been detected and characterized in human term placenta. The extract was found to contain very low levels of activity with an alkaline pH optimum. Western blotting demonstrated a polypeptide of Mr 26,000, instead of the subunit of Mr 36,000 observed in native mammalian Fru-P₂ases.     

Demonstration of fructose 1,6-bisphosphatase in human term placenta.

A proteolysed form of fructose 1,6-bisphosphatase (Fru-P2ase) has been detected and characterized in human term placenta. The extract was found to contain very low levels of activity with an alkaline pH optimum. Western blotting demonstrated a polypeptide of Mr 26,000, instead of the subunit of Mr 36,000 observed in native mammalian Fru-P2ases.     

Functional consequences of treating turkey liver fructose-1,6-bisphosphatase with penicillin G

Summary Treatment of turkey liver fructose-1,6-bisphosphatase with penicillin G progressively inactivated the enzyme and desensitized the enzyme toward high substrate inhibition. The treatment also led to reduced sensitivity to AMP inhibition and the loss of cooperative interaction among AMP-binding sites. These altered properties were not reversed by dialysis, but were prevented when treatment with penicillin G was performed in the presence of substrate.This work was in part supported by grant RR-8006 from the General Research Branch, Division of Research Resources, NIH (USA) and in part by Faculty Research Grant from Southern School of Pharmacy, Mercer University, Atlanta (Georgia, USA).     

Functional consequences of treating turkey liver fructose-1,6-bisphosphatase with penicillin G.

Treatment of turkey liver fructose-1,6--bisphosphatase with penicillin G progressively inactivated the enzyme and desensitized the enzyme toward high substrate inhibition. The treatment also led to reduced sensitivity to AMP inhibition and the loss of cooperative interaction among AMP-binding sites. These altered properties were not reversed by dialysis, but were prevented when treatment with penicillin G was perfomed in the presence of substrate.     

Effects of Mn2+ and Mg2+ on the pigeon liver pyruvate kinase

Riassunto Mn²⁺ and Mg²⁺ attivano la piruvato cinasi di fegato di piccione in maniera distinta. In presenza di basse concentrationi di fosfoenolpiruvato Mn⁺ é piú efficace di Mg²⁺ ed é attivatore dell'enzima saturato da Mg²⁺. Piruvato cinasi (EC 2.7.1.40).

---

---

This work was supported by a grant from the Consiglio Nazionale delle Ricerche, Roma, Italia.Silvia Baldi is a fellow of the Italian C.N.R.     

Inhibition of phosphoglucomutase by galactose 1,6-diphosphate

Zusammenfassung Chemisch synthetisiertes Galaktose-1,6-Diphosphat wird als Hemmer dès Glukose-1,6-Di-phosphats in der Phosphoglukomutase-Reaktion bestimmt.     

Inhibition of the infective activity of bacteriophage f2 by spermine

Résumé La spermine a un effet inhibiteur sur la reproduction du phage f₂. Cette inhibition dépend de la concentration de la spermine. Ne diminuant pas le taux du phage libre et n'ayant pas d'effet sur l'adsorption, la spermine réduit l'activité de l'ARN infectieuse et la production du phage dans les sphéroplastes infectés.     

Inhibition of rat liver transglutaminase by nucleotides

Summary Tissue-type transglutaminase (TGase) was purified from rat liver, and the effects of nucleotides on its activity were examined. The enzyme activity is inhibited by ATP in a concentration-dependent way, with complete inhibition by 3 mM ATP. Partially-purified TGase from human brain was inhibited by ATP in a manner similar to that observed with the rat liver enzyme. This suggests that the inhibition is a common phenomenon for tissue-type TGase in all species and tissues. The inhibition is reversible since full activity is restored by lowering the ATP concentration. CTP has a TGase-inhibitory potency equivalent to that of ATP, whereas GTP and UTP possess about 50% of the inhibitory activity of ATP. ADP inhibits TGase activity to the same extent as ATP, but AMP causes much less inhibition, and there is no inhibition by adenosine or adenine. The inhibition by ATP is insensitive to ionic strength and is non-competitive with the substrate putrescine. Since ATP levels in cells are of mM order, these results suggest that TGase activity is controlled by ATP in vivo.     

Inhibition of rat liver transglutaminase by nucleotides.

Tissue-type transglutaminase (TGase) was purified from rat liver, and the effects of nucleotides on its activity were examined. The enzyme activity is inhibited by ATP in a concentration-dependent way, with complete inhibition by 3 mM ATP. Partially-purified TGase from human brain was inhibited by ATP in a manner similar to that observed with the rat liver enzyme. This suggests that the inhibition is a common phenomenon for tissue-type TGase in all species and tissues. The inhibition is reversible since full activity is restored by lowering the ATP concentration. CTP has a TGase-inhibitory potency equivalent to that of ATP, whereas GTP and UTP possess about 50% of the inhibitory activity of ATP. ADP inhibits TGase activity to the same extent as ATP, but AMP causes much less inhibition, and there is no inhibition by adenosine or adenine. The inhibition by ATP is insensitive to ionic strength and is non-competitive with the substrate putrescine. Since ATP levels in cells are of mM order, these results suggest that TGase activity is controlled by ATP in vivo.     

Inhibition of Ca2+-induced noradrenaline release from central noradrenergic neurons by morphine

Summary Morphine inhibited the noradrenaline release from slices of rat brain cortex induced by introduction of Ca²⁺ ions after superfusion with Ca²⁺-free, K⁺-rich solution. The degree of inhibition was inversely related to the Ca²⁺ concentration used for stimulation.Acknowledgment. We thank Mrs G. Thielecke and Miss G. Werthmann for technical assistance.     

Inhibition of RNA polymerase activity by arginine-rich histones

Zusammenfassung Im Komplex mit der DNS-Matrize zeigt die lysinreiche Fraktion F1 eine doppelt so grosse Hemmung der RNS-Synthese in vitro als das argininreiche Histon F3. Demgegenüber erwies sich das argininreiche Histon F3, mit RNS-Polymerase komplexiert, wirksamer als das lysinreiche Histon F1, das heisst, dass die Inhibition mit dem argininreichen Histon F3 fünffache Steigerung und damit doppelte Wirksamkeit gegenüber F1 ergibt.