Thermal Aggregation of Cod (Gadus morhua) Muscle Proteins Using l-Ethyl-3-(3-Dimethylaminopropyl) Carbodiimide as a Zero Length Cross-linker

Abstract

The initial stages of thermally-induced aggregation of cod myofibrils resulted from noncovalent in ter molecular cross-linking as demonstrated by SDS electrophoresis. The nature of the noncovalent bonds was studied by introducing a zero length cross-linker, l-ethyl-3-(3-dimethylamino propyl) carbodiimide (EDC). This allowed the examination of the noncovalent interactions by SDS electrophoresis and quantitative densitometry. Initially, during heating, about 50% of the myosin heavy chain was cross-linked to form a polymerized complex before the involvement of actin, regulatory proteins, or the myosin light chains. Inhibition of thermally-induced noncovalent cross-linking with triglycerides or Triton X-100 as well as the enhancement of aggregation at higher ionic strength, suggested the importance of hydrophobic interaction in this reaction.

Cod myosin heavy chains were prepared and the head regions labelled with the fluorescent probe,,N-[7(dimethylamino)-4-methyl-3-coumarinyl] maleimide (DACM) which reacts specifically with two thiol groups near the active sites for Ca²⁺ and EDTA-ATPase. Chymotryptic cleavage of the thermally aggregated myosin heavy chains suggested the involvement of the tail region of the molecule rather than the head in the noncovalent cross-linking reactions.