Molecular weight of (sodium(1+), potassium(1+) ion)-stimulated ATPase from shark rectal gland

Abstract

The (Na+,k+)ATPase from the rectal gland of Carcharhinus obscurus has been solubilized in Lubrol WX as an active complex containing 379,900 g of protein and 61 mol of phospholipid. This detergent-lipid-protein complex contains two catalytic subunits of molecular weight 106,400 and four glycopeptide subunits of protein molecular weight 36,600. The latter subunit has a total molecular weight of 51,700 when the carbohydrate is included. Attempts to dissociate this active enzyme complex to smaller size by increasing the detergent concentration led to inactivation. Thus, the smallest active particle in the presence of Lubrol WX contains the two polypeptide subunits in a mole ratio of 2:4 under conditions where the micellar form of detergent is present at a 70:1 molar ratio. This large excess of Lubrol WX eliminates any possibility of artificial togetherness as the result of statistical considerations.

Mechanism of Free Energy Coupling in Active Transport

“…Boyer's mechanism for A TP processing in F of b discussed earlier, is an example of such a need. In the case of the Na,+K + pump, support fo r a dimeric functional unit is perhaps indicated by attempts to solubilize the protein in benign detergents with retention of ATPase activity; active preparations obtained so far are in a dimeric state (190,191). The alternating access model in its simplest form would require ApK.…”

The Structure of Proteins Involved in Active Membrane Transport

“…Only about 90, however, are needed for proper functioning. Purified enzyme from S. acanthias or Carcharhinus obscurus has about 60 moles of phospholipid bound to each 300,000 g protein (48,67).…”

Oligomeric Structure of Solubilized Na+/K+ ‐ATPase Linked to E1/E2 Conformation

“…The quaternary structure of Na + /K + ‐ATPase has been studied by solubilizing the membrane‐bound enzyme, purified from mammalian kidneys, with nonionic surfactants such as C 12 E 8 and Lubrol 1–6 . These studies have shown consistently that the two polypeptides, α and β, are noncovalently combined in a minimum structural unit, an αβ‐protomer.…”