Catalyic and regulatory properties of muscle pyruvate kinase fromCancer magister

✍ Scribed by Guderley, Helga ;Hochachka, Peter W.

• Publisher: John Wiley and Sons
• Year: 1980
• Tongue: English
• Weight: 729 KB
• Volume: 212
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402120318

✦ Synopsis

Abstract

Despite the marked changes that crustacean muscle undergoes during the molt cycle, pyruvate kinase is present as the same from throughout the molt cycle. This pyruvate kinase was subject to feed‐forvard activation by fructose‐1, 6 bisphosphate (FBP) as well as feed‐back inhibition by MgATP. The enzyme showed a high affinity for phosphoenolpyruvate (K~m~ = 0.1 mM) but showed no cooperativity in substrate binding. The addition of 0.05 mM FBP reduced the PEP K~m~ to 0.05 mM. MgATP inhibition showed a K~i~ of 1.8 mM versus PEP. The inhibition due to MgATP could be reversed by FBP. Various other compounds inhibited the enzyme, including citrate, α‐ketoglutarate, tryptophan, and malate, although at rather high levels. Measurements of the reversal of this pyruvate kinase, taken together with the low levels of phosphoenolpyruvate carboxykinase and pyruvate carboxylase, predict only minimal levels of gluconeogenic flux in crustacean muscle.