The effects of decreased aeration on the electron transport system and glyconeogenesis during growth of Tetrahymena pyriformis

Growth-dependent factors in the regulation of aminoacyl-tRNA synthetase activities of Tetrahymena pyriformis

Changes in phenylalanyl-tRNA synthetase (L-phenylalanine : tRNAPhe ligase, EC 6.1.1.20) and leucyl-tRNA synthetase (L-leucine : tRNALeu ligase. EC 6.1.1.4) activities were studied during the growth cycle of Tetrahymena pyriformis. High levels of charged tRNA observed during exponential growth were associated with elevated aminoacyl-tRNA synthetase activities. Low levels of charges tRNA in the stationary phase culture were associated with decreased aminoacyl-tRNA synthethase activities together with a concomitant accumulation of factor(s) which inhibited the enzyme activities. The inhibitory factor(s) has been partially purified and evidence is presented to rule out RNA, RNAases, proteases and ATPases as the responsible inhibitory factor(s) of the aminoacyl-tRNA synthetases.

Changes in cyclic AMP-dependent protein dinase activity in Tetrahymena pyriformis during the growth cycle

An adenosine 3':5'-monophosphate-dependent protein kinase II (ATP:protein phosphotransferase, EC 2.7.1.37) was partially purified from the cytosol fraction of an exponentially growing culture of Tetrahymena pyriformis. Protein kinase II represented approximately 90% of the cytosolic protein kinase activity. The enzyme had a high degree of substrate specificity for calf thymus and Tetrahymena histones as compared to casein, protamine and phosvitin. The enzyme incorporated the terminal phosphate of ATP into serine and threonine residues of all the histone fractions. The apparent Km of the enzyme for adenosine 3':5'-monophosphate (cyclic AMP) was 1-10-minus 8 M. Protein kinase II was also activated by other cyclic nucleotides with apparent Km values in the range 2.k-10-minus 6 M. Ther specific activity of the cyclic AMP-dependent protein kinase of Tetrahymena decreases markedly from initial high values during the transition from the lag to early log phase of growth. This is followed by a shrp increase in the activity of the enzyme as the log phase of growth progresses. The specific activity of the enzyme increases rapidly during the heat-induced synchronization of Tetrahymena cells. The capacity for rapid phosphorylation of multiple classed of organelle-specific phosphoproteins and the level of cyclic AMP were maximal in Tetrahymena during the earliest phase of growth. These results demonstrate that the cell cycle of Tetrahymena may be coordinated by marked variations in the level of cyclic AMP which in turn regulate the cyclic AMP-dependent protein kinase.