The value of galactose phosphate determinations in the treatment of galactosaemia.

Hereditary galactosaemia is now known to be due to the deficiency of a single enzyme, galactose-lphosphate uridyl transferase* (Kalckar, Anderson and Isselbacher, 1956). This enzyme, the second in the chain of three enzymes concerned with the metabolism of galactose, catalyses the conversion of gal-I-P to G-1-P, as shown in equation (2): gal + ATP gal-I-P + ADP (1) gal-i-P + UDPG = G-1-P + UDPgal (2) UDPgal = UDPG (3) The block in galactose metabolism at step (2) would be expected to lead to an accumulation of gal-l-P when galactosaemic individuals ingest galactose. An accumulation of this phosphate has been demonstrated in the erythrocytes of untreated infants suffering from galactosaemia, or in the erythrocytes of treated cases after incubation with galactose in vitro (Schwarz, Golberg, Komrower and Holzel, 1956; Kalckar et al., 1956). A diagnostic test for galactosaemia, based on this observation, has been reported previously (Schwarz, Holzel and Komrower, 1958). The intracellular accumulation of gal-l-P appears to lead to a serious disturbance of erythrocyte metabolism, as indicated by a fall in the respiratory rate and by a general derangement of phosphate metabolism (Schwarz et al., 1956; Komrower, Schwarz, Holzel and Golberg, 1956; Penington and Prankerd, 1958). An analogous disturbance has been demonstrated in a mutant of E. coli deficient in uridyltransferase: on incubation of the culture with galactose, it evinces a prolonged lag phase before the onset of growth, which is preceded by intracellular accumulation of gal-i-P (Kurahashi and Wahba, 1958). Recently evidence has been presented which indicates that gal-i-P may exert an inhibitory effect on a number of enzymes-phosphoglucomutase, G-6-P phosphatase and dehydrogenase (Sidbury, 1957; Ginsburg and Neufeld, 1957; Lerman, 1960). So far gal-l-P has been demonstrated only in the erythrocytes of galactosaemic infants. The liver, being the main site at which galactose is normally metabolized, would be expected to show a similar, or even greater, accumulation of this phosphate. Theoretically, all cells of the body are endowed, to a greater or lesser extent, with all enzymes and a hereditary deficiency in one enzyme might therefore make itself felt in all tissues. The purpose of this communication is threefold: to demonstrate that gal-I-P does, in fact, accumulate in several, if not all, tissues; to draw attention to the value of assessing erythrocyte gal-l-P at regular intervals as a guide to the adequacy of treatment; to present an improved method for the determination of gal-i-P. The gal-I-P values reported below were obtained by the method published previously (Schwarz et al., 1958). Since this method was evolved and most of the determinations made, pure gal-i-P has become available, thus permitting an assessment of the efficiency of its determination. Recent experiments have shown that the original method may involve losses of galactose resulting from irreversible adsorption on, or entrainment in, the salts left after evaporation to dryness. To overcome this defect as far as possible, and still retain the specificity of the method accruing from chromatographic separation of galactose from other carbohydrate or reducing substances, the following method has been devised. Determination of Gal-l-P Heparinized venous blood (about 2 ml.) which may be kept in ice (not frozen) for a few hours, is centrifuged