title: An adenosine triphosphate-dependent calcium uptake pump in human neutrophil lysosomes.
abstract: Regulation of the cytosolic free calcium concentration is important to neutrophil function. In these studies, an ATP-dependent calcium uptake pump has been identified in human neutrophil lysosomes. This energy-dependent Ca++ uptake pump has a high affinity for Ca++ (Michaelis constant [Km] Ca++ = 107 nM) and a maximum velocity (Vmax) of 5.3 pmol/mg of protein per min. ATP was the only nucleotide that supported Ca++ uptake by lysosomes. The Km for ATP was 177 microM. ATP-dependent Ca++ uptake by neutrophil lysosomes was temperature- and pH-sensitive with optimal Ca++ pump activity at 37 degrees C and pH 7.0-7.5. Mg++ was also essential for ATP-dependent Ca++ uptake by lysosomes. Azide and antimycin A had no effect on the energy-dependent uptake of Ca++ by neutrophil lysosomes. The chemotactic peptide formyl-methionyl-leucyl-phenylalanine inhibited ATP-dependent Ca++ accumulation by isolated lysosomes. Butoxycarbonyl-phenylalanine-leucine-phenylalanine-leucine-phenylalanine , a competitive antagonist of the chemotactic peptide, blocked this inhibitory effect. These studies demonstrate the presence of an ATP-dependent Ca++ uptake pump in human neutrophil lysosomes that functions at physiologic intracellular concentrations of Ca++, ATP, and H+ and may be important to regulating neutrophil function by modulating cytosolic Ca++.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001693:Biological Transport, Active; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000378:metabolism* / Q000648:ultrastructure; D009711:Nucleotides / Q000378:metabolism; D010539:Permeability
chemical_list: D009711:Nucleotides; D000001:Calcimycin; D009240:N-Formylmethionine Leucyl-Phenylalanine; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium