ISSN:
1432-1351
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary The naupliar stage ofArtemia salina has been found to contain large amounts of an ATPase which requires the presence of Mg++, is stimulated by Na+ and K+, and is sensitive to ouabain. Upon cell fractionation, sixty percent of the Na+K-activated ATPase activity was present in a heavy membrane fraction which accompanied mitochondria, and twenty percent of the activity was found in the microsomal fraction. Separation of the heavy membranes containing the Na+K-activated ATPase from mitochondria was accomplished by sucrose density gradient centrifugation. Kinetic characterization of the Na+K-activated ATPase was examined with both mitochondrial and microsomal preparations. No significant differences were observed between the two preparations. Maximal enzyme activity occurred at pH 7.2 and a temperature of 45 ° C. Half maximal inhibition of enzymatic activity occurred with ouabain concentration of 8 × 10−6 M. Half maximal activation of the enzyme by ATP and MgCl2 occurred at 8 × 10−4 and 1 × 10−3 M, respectively, with an optimal Mg++/ATP ratio of 2.0. NaCl and KC1 (or NH4C1) were required for activity, with half maximal activation at 1 × 10−2 and 9 × 10−3 M (or 2.1 × 10−2 M), respectively. The optimal Na+/K+ ratio was 4.0, although enzymatic activity occurred through a wide range of ratios. In contrast, survival of nauplii was reduced in media in which the Na+/K+ ratio was less than 10. Anatomical localization of the enzyme in nauplii indicated that the abdominal region contained 44% of the total Na+K-activated ATPase activity, while the cephalothoracic region contained 54% of the total activity. Isolated larval salt glands contained 10% or less of the total activity. In contrast, the adult leg segments containing the salt-transporting organs showed 54% of the total Na+K-activated ATPase activity.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00697956
