of O n l f f o r n h , Bcrki.lry FIVE FIGURES
INTRODITCTION
Compared with classic materials like yeast and vertebrate muscle, ciliated epithelium exemplified by the mollusk gill has received little attention in studies of metabolism. The gill of Pecteaz is known to contain glycogen and to produce lactic acid (Gray, 'as), and it is probable that its glycolytic processes are like those of tlie more intensirely studied inaterials. If this is true, then phosphate riinst play an cstrcmely important part in cellular metabolism, just as in vertebrate muscle, f o r physical activity in the ciliated tissue is coilstantly in evidence, necessitating a continual conversion of chemical to mechanical energy. Adenosine 1 riphosphate (ATP) or an ATP-like substance is probably present, though yet undescribed, arid tlie place of creatine as a bearer of energy-rich phosphate in vertebrate muscle is thought t o be taken in the inollusk by arginine (Florkin, '49). I n addition to these compounds it is safe to suppose the presence of phosphorus-containiii~ iiucleotides and phospliaticlcs.
Hevesy and co-workers (Hevesy, '47) h a w shown that intracellular pliosphatc is in a dyiiamic state: there is a constant interchange of individual phosphate moieties teniporarily bound to organic molecules, with others temporarily frce. It is kiiowri that the rate of turnorcr for ATP-phos-Prescnt address : Department of Biological Sciences, U n i T ersity of Delaware.