Calcium/calmodulin dependence of nitric oxide synthase from Viviparus ater immunocytes

Authors

  • D Tagliazucchi Department of Agricultural Sciences, University of Modena and Reggio Emilia, Italy
  • A Conte Department of Agricultural Sciences, University of Modena and Reggio Emilia, Italy

Keywords:

mollusc, Viviparus ater, immunocytes, nitric oxide synthase, calcium ion dependence

Abstract

The calcium ion dependence of soluble and particulate nitric oxyde synthase (NOS) activity from
Viviparus ater immunocytes was investigated. At a calcium ion concentration of 2 nM, the NOS activity measured by citrulline formation was 27.1 ± 2.2 and 9.3 ± 0.8 pmol/min/106 cell for soluble and particulate NOS, respectively. The increase in free calcium ion concentration to 300 nM increases enzyme activity to 57.5 ± 4.1 and 23.5 ± 1.2 pmol/min/106 cell, respectively. The 50 % activation of the calcium-dependent activity is 91 and 97 nM Ca2+ for soluble and particulate enzymes. Trifluoperazine, an inhibitor of the calmodulin-dependent enzyme, partially inhibits both activities. Soluble NOS is five times more sensitive than particulate NOS. The behaviour of both activities with three NOS inhibitors (7-nitroindazole, S-methylisothiourea sulphate, diphenyleneiodonium) is very similar, with IC50 values that are not significantly different. The calcium ion dependence of NOS activities, in a range of free calcium ion variations, which are transiently observed in receptor-stimulated cells, suggests that nitric oxyde in V. ater immunocytes not only has a defensive role but also signalling relevance in crosstalking between immunocytes and other cells.

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Published

2005-04-18

Issue

Section

Short Communications