Abstract
The glucan specifity of the purified chloroplast and non-chloroplast forms of α-1,4-glucan phosphorylase (EC 2.4.1.1) from spinach leaves (Steup and E. Latzko (1979), Planta 145, 69–75) was investigated. Phosphorolysis by the two enzymes was studied using a series of linear maltodextrins (degree of polymerization ≦11), amylose, amylopectin, starch, and glycogen as substrates. For all unbranched glucans (amylose and maltodextrins G5–G11), the chloroplast phosphorylase had a 7–10-fold higher apparent affinity (determined by initial velocity measurements) than the non-chloroplast phosphorylase form. For both enzyme forms, the minimum chain length required for a significant rate of phosphorolysis was five glucose units. Likewise, phosphorolysis ceased when the maltodextrin was converted to maltotetraose. With the chloroplast phosphorylase, maltotetraose was a linear competitive inhibitor with respect to amylose or starch (K i-0.1 mmol 1-1); the inhibition by maltotetraose was less pronounced with the non-chloroplast enzyme. In contrast to unbranched glucans, the non-chloroplast phosphorylase exhibited a 40-, 50-, and 300-fold higher apparent affinity for amylopectin, starch, and glycogen, respectively, than the chloroplast enzyme. With respect to these kinetic properties the chloroplast phosphorylase resembled the type of “maltodextrin phosphorylase”.
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Abbreviations
- G1P:
-
Glucose 1-phosphate
- MES:
-
2(N-morpholino)ethane sulphonic acid
- Pi :
-
orthophosphate
- Tris:
-
Tris(hydroxymethyl)aminomethane
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Steup, M., Schächtele, C. Mode of glucan degradation by purified phosphorylase forms from spinach leaves. Planta 153, 351–361 (1981). https://doi.org/10.1007/BF00384254
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DOI: https://doi.org/10.1007/BF00384254