Glycerol kinase (GK) is a key enzyme in glycerol metabolism with two alternatively spliced forms-one with an 87 bp insertion corresponding to exon 18 (GK+EX18), and one lacking exon 18 (GK-EX18). We report the expression of GK EX18 in various tissues and cell lines, as well as their enzymatic characteristics and subcellular localization. RT-PCR revealed differential expression in tissues and cell lines. Northern blot analysis revealed that both forms of the murine ortholog, Gyk, were highly expressed in murine heart and increased during embryonic development. K-m values for glycerol for GK EX18 were not significantly different, although GK-EX18 had a higher V-max for glycerol. GK-EX18 had a lower K-m and V-max for ATP than GK+EX18. Immunofluorescence experiments showed that GK+EX18 co-localized to the mitochondria and the perinuclear region while GK-EX18 had a diffuse expression pattern. These data suggest specific and divergent roles for GK+EX18 and GK-EX18 in cellular metabolism and development. © 2005 Elsevier Inc. All rights reserved.