title: Hexokinase present in human sperm is not tyrosine phosphorylated but its antibodies affect fertilizing capacity.
abstract: The present study was conducted to investigate the presence of hexokinase in human sperm cell, its subcellular localization, its modulation and role in capacitation/acrosome reaction, and tyrosine kinase activity, if any. These studies were conducted using antibodies (Ab) raised against rat brain hexokinase (type I isozyme) that have significant cross-reaction with various human tissue hexokinases and neutralize the catalytic activity of the enzyme. Hexokinase Ab reacted with acrosomal, mid-piece and tail regions of methanol-fixed (approximately 70-80%) and live (approximately 35-52%) sperm in the indirect immunofluorescence technique (IFT) and the immunobead binding technique (IBT), respectively. Hexokinase Ab specifically recognized a band of 116 kDa on the Western blot of detergent-solubilized human sperm preparation that was different from the 95-kDa phosphotyrosine protein. Hexokinase Ab caused a significant (P < 0.01 to < 0.001) and concentration-dependent inhibition of human sperm penetration of zona-free hamster oocytes in the sperm penetration assay (SPA). These data indicate that the hexokinase of 116-kDa molecular weight is present in acrosomal, mid-piece, and tail regions of human sperm. The sperm hexokinase is a glycoprotein that is different from the 95-kDa phosphotyrosine protein and is not phosphorylated at tyrosine residues; however, its antibodies cause agglutination and a concentration-dependent inhibition of fertilizing capacity of human sperm.
authors.affiliation: Department of Obstetrics and Gynecology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: R K
authors.initials: RK
authors.lastname: Naz
authors.forename: C
authors.initials: C
authors.lastname: Morte
authors.forename: K
authors.initials: K
authors.lastname: Ahmad
authors.forename: P
authors.initials: P
authors.lastname: Martinez
mesh_terms: D000906:Antibodies / Q000032:analysis; D015153:Blotting, Western; D003429:Cross Reactions; D005260:Female; D005306:Fertilization / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D006593:Hexokinase / Q000032:analysis* / Q000276:immunology; D006801:Humans; D008297:Male; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000737:chemistry; D013075:Sperm Capacitation / Q000502:physiology; D013084:Sperm-Ovum Interactions / Q000502:physiology; D013094:Spermatozoa / Q000201:enzymology* / Q000502:physiology / Q000648:ultrastructure
chemical_list: D000906:Antibodies; D006593:Hexokinase; D011505:Protein-Tyrosine Kinases