Catalase activity was determined in human semen by measuring the oxygen burst with a Clark electrode, after H2O2 addition. Significant catalase activities (mean +/- SD) were found in migrated, motile spermatozoa (44 +/- 17 nmoles O2/min/10(8) cells) and in seminal plasma of normozoospermic men (129 +/- 59 nmoles O2/min/ml). It has been demonstrated that seminal catalase originated from prostate; however, its activity was not correlated with the usual prostatic markers (such as citric acid and zinc). Our data suggest a multiglandular function secreted by this organ. The catalase activities measured in seminal samples from asthenozoospermic, infertile men were found lower than those from normozoospermic subjects. The understanding of the relative contribution of the different enzyme systems against O2 toxicity (superoxide dismutase, catalase, glutathione peroxidase) seem to be a priority area of research to understand disturbances of sperm function.

Eukaryotic microorganisms, as well as higher animals and plants, display many autonomous physiological and biochemical rhythmicities having periods approximating 24 hours. In an attempt to determine the nature of the timing mechanisms that are responsible for these circadian periodicities, two primary operational assumptions were postulated. Both the perturbation of a putative element of a circadian clock within its normal oscillatory range and the direct activation as well as the inhibition of such an element should yield a phase shift of an overt rhythm generated by the underlying oscillator. Results of experiments conducted in the flagellate Euglena suggest that nicotinamide adenine dinucleotide (NAD+), the mitochondrial Ca2+-transport system, Ca2+, calmodulin, NAD+ kinase, and NADP+ phosphatase represent clock "gears" that, in ensemble, might constitute a self-sustained circadian oscillating loop in this and other organisms.

NAD kinase is thought to play an important role in the plant cellular responses to biotic and abiotic stress as one of the isoforms of the enzyme is activated by the Ca 2+ -calmodulin (CaM) complex. NAD kinase activity was measured after short-term NaCl stress applied to isolated cells from Lycopersicon esculentum, var. Volgogradskij (NaClsensitive tomato) and L. pimpinellifolium, acc. PE2 (NaCltolerant species). NAD kinase activity remained constant in the sensitive species, whereas a sharp decrease was observed in the tolerant one. After salt treatment, an induction of the calmodulin gene(s) was observed in the two species, together with a 30-50% decrease in 'active' CaM content, i.e. CaM able to activate purified NAD kinase, in L. pimpinellifolium. The decrease in NAD kinase activity could not, however, be fully explained by this decrease in active CaM content. A similar decrease in NAD kinase activity was also recorded with other ionic stresses and exposure to high temperatures, but not in the case of drought, exposure to low temperatures, hormonal (indole-3-acetic acid and abscisic acid) or H 2 O 2 treatments. External Ca 2+ certainly plays a role in the biochemical mechanism(s) leading to NAD kinase inhibition, while no role could be shown for intracellular Ca 2+. In addition, after salt stress, a modification of the redox state of NAD kinase seems to be responsible for the inhibition of the enzyme.

Two NADPH-dependent disulfide reductases, glutathione reductase and trypanothione reductase, were shown to be present in Euglena gracilis, purified to homogeneity and characterized. The glutathione reductase (M r 50 kDa) displays a high specificity towards glutathione disulfide with a K w of 54 W WM. The amino acid sequences of two peptides derived from the trypanothione reductase (M r 54 kDa) show a high level of identity (81% and 64%) with sequences of trypanothione reductases from trypanosomatids. The trypanothione reductase is able to efficiently reduce trypanothione disulfide (K w 30.5 W WM) and glutathionylspermidine disulfide (K w 90.6 W WM) but not glutathione disulfide, nor Escherichia coli thioredoxin disulfide, nor 5,5P-dithiobis(2-nitrobenzoate) (DTNB). These results demonstrate for the first time (i) the existence of trypanothione reductase in a non-trypanosomatid organism and (ii) the coexistence of trypanothione reductase and glutathione reductase in E. gracilis.z 1999 Federation of European Biochemical Societies.