Isoforms of Na,K-ATPase inArtemia saline: I. Detection by FITC binding and time course
Partially purified Na,K-ATPase from whole nauplii at various stages of development, analyzed by SDS-PAGE, reveals a polydisperse β and two α subunits (denoted α1 and α2). In the absence of Ca2+, ATP-inhibitable fluorescein isothiocyanate (FITC) labeling is restricted to the α subunit of this enzyme, even in crude naupliar homogenates. The intensity of the α-specific fluorescent signal (i.e., the sum of the yield from both α isoforms) is proportional to Na,K-ATPase activity during development. FITC-labeled subunits were detected at 8 hr of development prior to the detection of measurable Na,K-ATPase activity. The α2/α1 ratio changed from an initial value of 1.25 to a peak of 1.75 at 32 hr of development, then reverted to a ratio of 1.25 by 42 hr, and remained constant thereafter. Pulse chase studies with35S-methionine indicated that the developmental increase in enzyme activity is coincident with amino acid incorporation into the α subunits, implying that enzyme synthesis is active during enzyme accumulation.
Key WordsNa,K-ATPase isoforms Artemia salina brine shrimp fluorescein isothiocyanate
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