The effects of thiourea and of several substituted thioureasphenylthiourea, a-naphtylthiourea, nietiamide, and burinianiide ~ on dynein ATPase have been studied. The substituted thioureas are over 30 times more potent than thiourea in causing enhancement of 30s dynein A'TPase activity and inhibition of 14s dynein ATPase activity. The effects of thiourea and phenylthiourea can be prevented by very low concentrations of P-mercaptoethanol o r ditliiothreitol. Axoneinal ATPase is also enhanced by the thioureas, hut the reaction proceeds inore slowly than for solubilized 3 0 s dynein. Enhancement of 3 0 s dynein ATPase by nietiamide is prevented by low (% 1pM) concentrations o f A'I'P and, less effectively, by AMP-PNP, but not by AhlP-PCP even thougli the latter is a stronger inhibitor of 3 0 s dynein ATPase than is AMP-PNP.
The thioureas inhibit the ATP-induced decrease i n turbidity (measured as A A 3 5 0 ) of axonemal suspensions. Inhibition of the turbidity response is also prevented by low concentrations of P-mercaptoethanol, but, in contrast t o the irreversible enhancement of Al'I'ase activity, inhibition of t h e turbidity response is largely reversible. The ability of 30s dynein t o rebind o n t o twiceextracted axonenies is not changed b y treatment with phenylthiourea or in e t ianii d e.
of SH or S-S groups on axoneiiies. Reaction with the group(s) on the 30s dynein C;ILIS~S an apparently irreversible enhancement of AlPase activity. Kraction with another group(s) causes a revcrsihle inhibition of the turbidity response.
'lhese observations indicate t h a t the thioureas react with at least two sets
Key words: thiourea, cilia, dyneins, ATPase, sulfllydryl groups, turbidity response
The finding [ 1, 21 that "1.0.5 M thiourea inhibited the actomyosin system of mollusc muscle but not the "catch" mechanism led Brokaw and his colleagues to study the effects of thiourea on flagellar motility. Brokaw found that ~0 . 2 M thiourea rapidly reduced the beat frequency o f Ciona and Lytechnius sperm with little change in other wave parameters. With increase o f the time of exposure t o thiourea, however, amplitude and fre-Abbrcvistions or generlc naiiics u w d arc: mctiamide, N-me thyl-N'(2 [ (5-1iietti~limidazol-4-~1) nleth>lltliioll ethyl) thiourea; burimamide. N-( -2-1 (i~iiidat-ol-4-yl)iiictIi~ltf~io] e t1iyl)-N'-niethylthiourea; 0-hlSH. ,:-mcri~a~~toetliatiol; D ' I I . ditliiotlireitol; .