scholarly journals The nature of the binding site for aromatic compounds in glycogen phosphorylase b

1975 ◽  
Vol 147 (2) ◽  
pp. 369-371 ◽  
Author(s):  
G Soman ◽  
G Philip
Keyword(s):  
Chemical Modification ◽  
Binding Site ◽  
Aromatic Compounds ◽  
Glycogen Phosphorylase ◽  
Relative Effectiveness ◽  
Rabbit Muscle ◽  
Substituent Constant ◽  
Chemically Modified ◽  
Glycogen Phosphorylase B ◽  
Hydrophobic Nature

The inhibition of rabbit muscle glycogen phosphorylase b (1,4-alpha-D-glucan--orthophosphate alpha-glucosyltransferase, EC 2.4.1.1) by aromatic compounds was examined with 15 compounds. The relative effectiveness of the inhibitors correlated well with increasing substituent constant, pi, indicating the hydrophobic nature of the binding site. The inhibition was not affected by the ionic-strength variation of the assay mixtures. The results predict that the course of chemical modification of this enzyme and the properties of the derivatives depend on the nature of the reagent and on the incorporated groups. Many of the dissimilar and sometimes contradictory results reported for chemical-modification studies and for chemically modified phosphorylase b are explained by the findings presented in the paper.

scholarly journals Homogeneous Enzyme Immunoassay for Triiodothyronine in Serum

2001 ◽  
Vol 47 (3) ◽  
pp. 569-574 ◽  
Author(s):  
Christina D Karapitta ◽  
Theodore G Sotiroudis ◽  
Athanassios Papadimitriou ◽  
Aristotelis Xenakis
Keyword(s):  
Enzyme Immunoassay ◽  
Glycogen Phosphorylase ◽  
Serum Proteins ◽  
Rabbit Muscle ◽  
Glycogen Phosphorylase B ◽  
Low Concentrations ◽  
Enzyme Conjugate ◽  
High Concentrations ◽  
Treatment Step ◽  
Homogeneous Enzyme Immunoassay

Abstract Background: The concentration of triiodothyronine (T3) in human serum is extremely low and can be determined only by very sensitive methods. We developed a homogeneous enzyme immunoassay for T3 analysis in unextracted serum. Methods: A T3 derivative was conjugated to the −SH groups of glycogen phosphorylase b (GPb) from rabbit muscle. Conjugation caused inhibition of enzyme activity, and the enzyme conjugate was reactivated upon binding of anti-T3 antibody. Activation was blocked by the presence of non-antibody-bound T3; this was the basis for the development of the homogeneous enzyme immunoassay for T3 by determining GPb activity fluorometrically. Results: We used furosemide to block the interaction of T3 with serum proteins with T3-binding sites, avoiding any serum treatment step. T3 was measured in the range 0.3–8 μg/L. T3 values obtained by this assay correlated well with those obtained by a RIA (y = 0.97x − 0.07 μg/L; r = 0.96; n = 92). Within- and between-run imprecision (CV) was 5–9% for normal and high concentrations and 16–20% for low concentrations. Conclusions: Chemical modification of GPb with a T3 derivative allows the development of a simple homogeneous enzyme immunoassay for T3 in unextracted serum.

scholarly journals Modification of Cys-837 identifies an actin-binding site in the beta-propeller protein scruin.

1997 ◽  
Vol 8 (3) ◽  
pp. 421-430 ◽  
Author(s):  
S Sun ◽  
M Footer ◽  
P Matsudaira
Keyword(s):  
Chemical Modification ◽  
Binding Site ◽  
Solvent Accessibility ◽  
The Other ◽  
Actin Binding ◽  
Binding Region ◽  
Binding Studies ◽  
Chemically Modified ◽  
Cross Links ◽  
Actin Binding Site

In the acrosomal process of Limulus sperm, the beta-propeller protein scruin cross-links actin into a crystalline bundle. To confirm that scruin has the topology of a beta-propeller protein and to understand how scruin binds actin, we compared the solvent accessibility of cysteine residues in scruin and the acrosomal process by chemical modification with (1,5-IAEDANS). In soluble scruin, the two most reactive cysteines of soluble scruin are C837 and C900, whereas C146, C333, and C683 are moderately reactive. This pattern of reactivity is consistent with the topology of a typical beta-propeller protein; all of the reactive cysteines map to putative loops and turns whereas the unreactive cysteines lie within the predicted interior of the protein. The chemical reactivities of cysteine in the acrosomal process implicate C837 at an actin-binding site. In contrast to soluble scruin, in the acrosomal process, C837 is completely unreactive while the other cysteines become less reactive. Binding studies of chemically modified scruin correlate the extent of modification at C837 with the extent of inhibition of actin binding. Furthermore, peptides corresponding to residues flanking C837 bind actin and narrow a possible actin-binding region to a KQK sequence. On the basis of these studies, our results suggest that an actin-binding site lies in the C-terminal domain of scruin and involves a putative loop defined by C837.

scholarly journals Allosteric interactions of glycogen phosphorylase b. A crystallographic study of glucose 6-phosphate and inorganic phosphate binding to di-imidate-cross-linked phosphorylase b

1984 ◽  
Vol 218 (1) ◽  
pp. 45-60 ◽  
Author(s):  
A Lorek ◽  
K S Wilson ◽  
M S P Sansom ◽  
D I Stuart ◽  
E A Stura ◽  
...  
Keyword(s):  
Binding Site ◽  
Conformational Changes ◽  
Inorganic Phosphate ◽  
Glycogen Phosphorylase ◽  
Phosphate Binding ◽  
Binding Studies ◽  
Structural Explanation ◽  
Alpha Helices ◽  
Allosteric Effector ◽  
Glycogen Phosphorylase B

The binding to glycogen phosphorylase b of glucose 6-phosphate and inorganic phosphate (respectively allosteric inhibitor and substrate/activator of the enzyme) were studied in the crystal at 0.3 nm (3A) resolution. Glucose 6-phosphate binds in the alpha-configuration at a site that is close to the AMP allosteric effector site at the subunit-subunit interface and promotes several conformational changes. The phosphate-binding site of the enzyme for glucose 6-phosphate involves contacts to two cationic residues, Arg-309 and Lys-247. This site is also occupied in the inorganic-phosphate-binding studies and is therefore identified as a high-affinity phosphate-binding site. It is distinct from the weaker phosphate-binding site of the enzyme for AMP, which is 0.27 nm (2.7A) away. The glucose moiety of glucose 6-phosphate and the adenosine moiety of AMP do not overlap. The results provide a structural explanation for the kinetic observations that glucose 6-phosphate inhibition of AMP activation of phosphorylase b is partially competitive and highly co-operative. The results suggest that the transmission of allosteric conformational changes involves an increase in affinity at phosphate-binding sites and relative movements of alpha-helices. In order to study glucose 6-phosphate and phosphate binding it was necessary to cross-link the crystals. The use of dimethyl malondi-imidate as a new cross-linking reagent in protein crystallography is discussed.

Sequence of the carboxyl-terminal 492 residues of rabbit muscle glycogen phosphorylase including the pyridoxal 5'-phosphate binding site

Biochemistry ◽  
1978 ◽  
Vol 17 (26) ◽  
pp. 5680-5695 ◽  
Author(s):  
Koite Titani ◽  
Atsushi Koide ◽  
Lowell H. Ericsson ◽  
Santosh Kumar ◽  
Jacques Hermann ◽  
...  
Keyword(s):  
Binding Site ◽  
Muscle Glycogen ◽  
Glycogen Phosphorylase ◽  
Rabbit Muscle ◽  
Phosphate Binding ◽  
Carboxyl Terminal
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