Thyroid hormone stimulates synthesis of a cardiac myosin isozyme. Comparison of the two-two-dimensional electrophoretic patterns of the cyanogen bromide peptides of cardiac myosin heavy chains from euthyroid and thyrotoxic rabbits.

I.L Flink,J.H Rader,E Morkin

doi:10.1016/s0021-9258(17)30188-6

Abstract

The CNBr peptides of [14C]carboxymethylated cardiac myosin heavy chains from euthyroid and thyrotoxic rabbits have been compared using a two-dimensional electrophoretic system. The results indicated that there were extensive differences in the peptide "maps" of these heavy chains, which included differences in the distribution of radiolabeled thiol peptides. Also, the patterns of heavy chain peptides from the cardiac myosins have been compared with those produced by the heavy chain myosin isozymes from skeletal muscles. Peptide maps of heavy chains from red skeletal muscle myosin closely resembled the pattern of peptides found with cardiac myosin heavy chains from euthyroid rabbits. However, peptide maps of heavy chains from white skeletal muscle myosin were dissimilar to those of the cardiac myosin isozymes. We conclude that thyroxine administration stimulates the synthesis of a cardiac myosin isozyme with a heavy chain primary structure which is different from either of the skeletal muscle myosin isozymes.

Highlights

From the Departments 85724 of Znternal Medicine and Pharmacology, University of Arizona College of Medicine, Tucson, Arizona
Peptide maps of heavy chains from red skeletal muscle myosin closely resembled the pattern of peptides found with cardiac myosin heavy chains from euthyroid rabbits
We conclude that thyroxine administration stimulates the synthesis of a cardiac myosin isozyme with a heavy chain primary structure which is different from either of the skeletal muscle myosin isozymes

Summary

Introduction

From the Departments 85724 of Znternal Medicine and Pharmacology, University of Arizona College of Medicine, Tucson, Arizona. The CNBr peptides of [14C]carboxymethylated cardiac myosin heavy chains from euthyroid and thyrotoxic rabbits have been compared using a two-dimensional electrophoretic system. We conclude that thyroxine administration stimulates the synthesis of a cardiac myosin isozyme with a heavy chain primary structure which is different from either of the skeletal muscle myosin isozymes. We have presented evidence that thyroxine produces this effect by inducing the synthesis of a myosin isozyme, myosin-C,,’ which has greater ATPase activity than the species normally present within the heart (myosin-C,) [6]. This conclusion was based on differences in the mobility of CNBr peptides from S-. We have compared the two-dimensional “maps” of the cardiac myosin isozymes with maps produced by the peptides from myosin-R and myosin-

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