Influence of temperature acclimatization on the ionic activation of goldfish intestinal adenosine triphosphatase.

1. An adenosine triphosphatase membrane system, dependent on Mg(2+) and activated further by Na(+)+K(+), was prepared from goldfish anterior intestine by differential centrifugation of homogenized intestinal scrapings. 2. The affinity of this preparation for Na(+) in the presence of K(+)+Mg(2+), for K(+) in the presence of Na(+)+Mg(2+) and for Mg(2+) alone, measured at 37 degrees , did not depend on the previous environmental temperature of the fish. When Na(+)+K(+) were added to preparations from 8 degrees -acclimatized fish the affinity for Mg(2+) increased; this was not seen with preparations from 30 degrees -acclimatized fish. 3. Part of the Mg(2+)-activated adenosine triphosphatase was inhibited by Na(+) and the amount of inhibition appeared to increase at high acclimatization temperatures. 4. This Na(+)-inhibited adenosine triphosphatase was separated from the (Na(+)+K(+))-activated enzyme by centrifugation on sucrose density gradients. 5. Preparations from 8 degrees -acclimatized fish contained less Mg(2+)-activated and more (Na(+)+K(+))-activated adenosine triphosphatase than did similar fractions from 30 degrees -acclimatized fish. 6. Acclimatization to different environmental temperatures might involve one form of adenosine triphosphatase changing to another. The origin of various membranes seen in microsomal fractions must, however, be established before this hypothesis can be tested further.