Changes in Hemoprotein Content in Tetrahymena pyriformis (Strain NT-1) as Studied by Low Temperature Spectroscopy

Abstract

Cytochromes in Tetrahymena pyriformis cultured under various growth conditions were analyzed by the aid of a low temperature spectroscopic technique which allowed us to quantitate the cytochrome contents in the whole cell. When the protozoa were grown in a nutrient-rich medium at 39.5°C, the presence was clearly demonstrated of two cytochromes with α-bands at 553 and 558 nm, respectively. By subcellular fractionation, the former cytochrome was shown to be located in the mitochondria, which also contained another cytochrome with its a-band at 548 nm, whereas the latter was from the microsomes.
When the cells were grown either in glucose-deficient medium or at 15°C, the total amounts of cytochromes were depressed significantly compared with those grown in the enriched medium, although the number of cell divisions and final cell densities were not markedly affected. Glucose-supplementation of the deficient medium after 36 h of incubation did not restore the cytochrome level. On the other hand, both the cytochrome contents and growth rate were significantly decreased in an iron-deficient medium. The addition of iron to the deficient medium resulted in an increase in the level of a cytochrome with α-band at 553 nm, but did not affect the level of other cytochromes or the growth rate.
On starvation of the cells in a minimum medium containing only phosphate and a few minerals, the cytochrome contents were remarkably diminished. Electron microscopic examination revealed that the starvation process was accompanied by decreases in cell size, the number of mitochondria, and the amounts of endoplasmic reticulum in the cell. On transferring the starved cells to the enriched medium, the levels of the mitochondrial 553-nm peak cytochrome increased concomitantly with an increase in mitochondrial number, then the microsomal cytochromes began to accumulate as a well-developed endoplasmic reticulum was restored.
Based on these findings, the regulation mechanism for the biosynthesis of subcellular organelles and their components is discussed. The mitochondrial function appears to be prerequisite for microsomal hemoprotein accumulation in this protozoon.