SOME OBSERVATIONS ON GLYCEROL-TREATED MUSCLE FIBERS

Abstract

1. Neither calcium nor manganese can take the place of magnesium in supplying the divalent ion requirement for pyrophosphate relaxation of glycerol-treated muscle fibers; in this respect pyrophosphate is similar to other relaxation factors of the “first” group: myokinase, the creatine-kinase system, and EDTA.
2. Cysteine causes a lengthening of contracted glycerinated fibers, which is accelerated by any one of these three bivalent cations (Mg⁺⁺, Ca⁺⁺ or Mn⁺⁺).
The lengthening caused by cysteine is also qualitatively different in other respects from that by other relaxation factors (including pyrophosphate), and may be additive to relaxations produced by them.
3. Mono-iodoacetate has a slight accelerating effect on shortening in the ATP+Mg⁺⁺ medium, it can stop cysteine lengthening, and it causes subsequent relaxation by the EDTA relaxation medium to be incomplete.
4. Old and well-washed glycerinated fibers (more than 60 days in 50 per cent glycerol-water at -10° and more than 10 hours washing in 160mM per liter KCl at 0°) relax only incompletely in the EDTA medium; this supports Ebashi's idea (6) that there is a second relaxation factor which is removed by the long preparation procedures.
5. The old well-washed fibers just described can be made to relax completely in the presence of cysteine and lower pH. However, some irreversible process is involved in such lengthening, which indicates that cysteine cannot function as the second relaxation factor.
6. DNP, KF, arsenate and arsenite have various but small inhibitory effects on the amount of shortening, but none on relaxation by EDTA.
We wish particularly to thank Dr. M. F. Morales (Naval Medical Research Institute, Bethesda, Maryland, U.S.A.) for many valuable suggestions and criticisms.