Abstract
Characterization of insulin-sensitive phosphodiesterase in fat cells. II. Comparison of enzyme activities stimulated by insulin and by isoproterenol.
Highlights
The stimulatory effects of insulin and certain lipolytic it is still obscure whether insulin and lipolytic agents would agents on CAMPphosphodiesterase were compared. produce identical or different forms of the activatedenzymes
General Characteristics of Phosphodiesterase Preparations Stimulated by Insulinand by Certain Lipolytic Agents-In the experiments summarized in Table I, we examined whether the effects of insulin andcertain lipolytic agents are additive
Based on our present study, we suggest that insulin and certain lipolytic agents, such as isoproterenol, stimulate the same species of phosphodiesterase rather than two different enzymes and produce identical activated species
Summary
The enzyme activity stimulated by insulin under optimum conditions did not increase any further by the addition of isoproterenol, adrenocorticotropin, dibutyryl CAMP,3-isobutyl-l-methylxanthineo,r theophylline. The basal, plus insulin, and plus isoproterenol activities were all associated with the endoplasmic reticulum. The plus insulin and plus isoproterenol activities showed almost identical responses with heat, salt, and several sulfhydryl-blocking agents. The solubilized enzyme retained the effects of According to Zinman and Hollenberg (1)and Solomon (2), the K,,, value of the basal enzyme and that of the enzyme preparations stimulated byinsulin or catecholamines were indistinguishable. The major aimof our present study is toexamine whether insulin and lipolytic hormones stimulate the samespecies of phosphodiesterase and produce identical forms of the activated enzymes. The apparent Stokes radii of the solubilized plus insulin and plus isoproterenol enzymes were both approximately 94 A, while that of the basal enzyme was approximately 87
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