Functional organization of mitotic microtubules. Physical chemistry of the in vivo equilibrium system

Biophys J. 1975 Jul;15(7):725-44. doi: 10.1016/S0006-3495(75)85850-4.


Equilibrium between mitotic microtubules and tubulin is analyzed, using birefringence of mitotic spindle to measure microtubule concentration in vivo. A newly designed temperature-controlled slide and miniature, thermostated hydrostatic pressure chamber permit rapid alteration of temperature and of pressure. Stress birefringence of the windows is minimized, and a system for rapid recording of compensation is incorporated, so that birefringence can be measured to 0.1 nm retardation every few seconds. Both temperature and pressure data yield thermodynamic values (delta H similar to 35 kcal/mol, delta S similar to 120 entropy units [eu], delta V similar to 400 ml/mol of subunit polymerized) consistent with the explanation that polymerization of tubulin is entropy driven and mediated by hydrophobic interactions. Kinetic data suggest pseudo-zero-order polymerization and depolymerization following rapid temperature shifts, and a pseudo-first-order depolymerization during anaphase at constant temperature. The equilibrium properties of the in vivo mitotic microtubules are compared with properties of isolated brain tubules.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Birefringence
  • Calorimetry
  • Female
  • Mathematics
  • Meiosis
  • Microtubules / physiology*
  • Microtubules / ultrastructure
  • Mitosis*
  • Muscle Proteins / physiology
  • Ovum / physiology
  • Ovum / ultrastructure
  • Pressure
  • Sea Urchins / physiology
  • Temperature
  • Thermodynamics
  • Time Factors


  • Muscle Proteins