53 zyxwvutsr Clinica Chimica A&a, 92 (1979) 53- 64 @ Elsevier/North-Holland Biomedical Press CGA 9876 THE ASSAY OF SPHINGOLIPID HYDROLASES IN WHITE BLOOD CELLS WITH LABELLED NATURAL SUBSTRATES LARS SVENNERHOLM *, GUNILLA HAKANSSON, JAN-ERIC MANSSON and MARIE THfiRlbE VANIER Department of Neurochemistry, Psychiatric Research Centre, University of Giiteborg, S:t Jergen Hospital, S-422 03 Hisings Backa (Sweden) (Received July 17th, 1978) Summary Methods were elaborated for the assay on leukocytes of sphingolipid hy- drolases with native and artificial substrates. The optimal conditions for the isolation of leukocytes and the preparation of labelled sphingolipids were investigated. The Khl and zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG Vmax values for all substrates are given as the specific activities of the sphingolipidhydrolases in normal males and females. It is concluded that leukocytes are the enzyme source of choice for the enzymic diagnosis of neurolipidoses. Introduction It is more than ten years since the first methods for the enzymic diagnosis of the neurolipidoses were described [l], yet only few systematic attempts have been made to find out the optimal assay conditions for the enzyme identifica- tion of affected homozygotes and/or to identify the carriers. In a recent article in this journal, Kolodny and Mumford [ 21 gave a survey of the assay of 11 acid hydrolases with the fluorogenic derivatives of 4-methylumbelliferone, and Glew and Peters [3] have edited a book on the assay of the sphingolipidoses with natural and synthetic substrates. This paper extends this information and dis- cusses not only the optimal assay conditions, but also Ku and V,,, values and the normal values of the sphingolipid hydrolases in leukocytes. When the present study was started five years ago we expected to find several different genotypes of each neurolipidosis in Scandinavia. In order to improve the discrimination between variant forms we decided to use both synthetic and natural substrates when feasible. The assays were applied on zyxwvuts * To whom correspondence should be addressed.