Tyrosine kinases and phosphatases in the estivating spadefoot toad

To endure seasonally arid conditions, spadefoot toads (Scaphiopus couchii) spend 9-10 months underground each year in a hypometabolic state, termed es tivation, Protein tyrosine kinases (PTKs) and phosphatases (PTPs) were eval uated in organs of control and estivating toads to assess their possible ro le in signal transduction during estivation, Total PTK activity decreased b y 27-52 % in liver, lung and skeletal muscle during estivation but rose by 66% in heart, Total PTP activity changed only in liver (55 % decrease) and heart (74 % increase), Analysis of the distribution of PTKs between cytopla smic and membrane-associated forms showed that estivation-link,ed changes i n both fractions occurred in heart (increase) and liver (decrease) whereas in lung and skeletal muscle only the soluble fraction was affected, PTPs we re assessed using both a general substrate (ENDpYINASL) and a substrate (DA DEpYLIPQQG) specific for PTPs containing the SH2 binding site; both reveale d estivation-associated changes in activities and subcellular distribution of PTPs in all tissues, C)EAE-Sephadex chromatography showed multiple forms of skeletal muscle PTKs and PTPs in both soluble and insoluble fractions, Each fraction showed three major peaks of PTK activity, two of which shifte d in elution position during estivation, The data show that PTKs and PTPs a re modified in an organ-specific fashion during estivation by three mechani sms: changes in total activity, changes in subcellular distribution and pos sible protein covalent modification, Copyright (C) 2001 S. Karger AG, Basel .