Abstract
Tubulin subjected to heat, urea, or guanidine hydrochloride treatment differed in some respects from native tubulin, which inhibits actomyosin Mg-adenosine triphosphatase (ATPase) activity and the corresponding turbidity change. Whereas native tubulin inhibited 65% of actomyosin Mg-ATPase activity, tubulin heated at 65-70°C for 3 min reduced the ATPase activity to 8% of the original level. The effective inhibition by tubulin was gradually diminished when tubulin was treated above 75°C. Since such treated tubulin had little effect on myosin Mg-ATPase activity, it seems to inhibit the actin activation through its binding to myosin. The changes of turbidity inhibition of actomyosin by tubulins were similar to those in ATPase inhibition. Heat treatment converted the conformation of tubulin from α-helix to β-structure, and heat-treated tubulin was easily degraded by trypsin. Tubulin denatured with urea or guanidine hydrochloride showed less ATPase inhibition than heat-treated tubulin.
