The biosynthesis of trehalose in the locust fat body.
Schi8tocerca gregaria, the haemolymph of which may contain up to 2 % of trehalose (Howden & Kilby, 1956). Treherne (1958a, b) demonstrated that the introduction of radioactive glucose into the alimentary canal or directly into the haemolymph of S. gregaria in vsvo resulted in the appearance of radioactive trehalose in the haemolymph within a short time, but the site and mode of conversion of glucose into trehalose were not investigated. We have been able to show that the fat body is the most active tissue of the locust in this respect. The insect fat body is a conspicuous organ which extends throughout the abdominal and thoracic cavities, and consists of a loose meshwork of anastomosing lobes formed of sheets of single or double layers of yellow cells. It occupies the space between the gut and the body wall and is everywhere in contact with the blood, so a ready interchange of metabolites between fat-body cells and the blood would be expected. One function of the fat body which has long been recognized is that of a storage organ, since the cells become loaded with globules of fat, protein and glycogen during the development of the insect. Recently it has been shown that fat-body tissue is active in carrying out a number of different metabolic reactions (Kilby & Neville, 1957; Bellamy, 1958; Zebe & McShan, 1959), and the organ may possibly be considered as an equivalent in some respects of the mammalian liver as a site of intermediary metabolism. For these reasons, it was thought that it might be involved in trehalose biosynthesis. Fat body forms a very convenient tissue for biochemical investigation as it is readily dissected from the insect and can be obtained almost free from other tissues. It was found that the fat body ofS. gregaria would convert radioactive glucose into trehalose in vitro, and the subsequent preparation of active cell-free extracts from it facilitated the study of the pathway of trehalose biosynthesis. Their yeast preparation also contained a specific phosphatase for trehalose phosphate. In the present paper we describe the identification of similar enzymes in the fat body of S. gregaria, and also of other enzymes for the regeneration of uridine diphosphate glucose and the formation of glucose 6-phosphate. Parts of this work have been briefly reported elsewhere (Candy & Kilby, 1959, 1960).