. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 0 2 04 06 ORNITHINE (mM) Figure 1. Activity of ornithine decarboxylase measured at various substrate (ornithine) concentrations and at assay temperatures of 0, 5, and 15°C. All assays were performed in duplicate. Many invertebrates are exposed to daily or seasonal changes in temperature and demonstrate temperature- dependent growth characteristics. Although temperature is often cited as an important modulator of growth, the mechanisms by which temperature-dependent growth is regulated remain obscure. We hypothesi
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 0 2 04 06 ORNITHINE (mM) Figure 1. Activity of ornithine decarboxylase measured at various substrate (ornithine) concentrations and at assay temperatures of 0, 5, and 15°C. All assays were performed in duplicate. Many invertebrates are exposed to daily or seasonal changes in temperature and demonstrate temperature- dependent growth characteristics. Although temperature is often cited as an important modulator of growth, the mechanisms by which temperature-dependent growth is regulated remain obscure. We hypothesize that tempera- ture regulation of ornithine decarboxylase activity and polyamine synthesis may be one mechanism by which temperature regulates growth in ectothermal organisms. In this study we report the effect of assay temperature on the kinetic characteristics of ornithine decarboxylase extracted from the testes of A vulgaris. Materials and Methods Adult specimens of Asterias vulgaris (8-10 cm arm length) were collected from a depth of 3 meters at the mouth of the Piscatequa River in Portsmouth, New Hampshire, in March 1987. Testes were removed from three individuals and pooled for ODC extraction and analysis. Fresh testes were homogenized (20% w:v, 1:4) on ice with a glass Teflon homogenizing apparatus in a buffer containing 50 mM KH2PO4, pH , mM EDTA, 5 mM dithiothreitol and 50 fiM pyridoxal 5-phosphate. The crude extract was centrifuged for 30 min at 20,000 X g at 0°C. The supernatant was used for enzyme activity determinations. The specific activity of ODC was determined by a pro- cedure modified from Landy-Otsuka and Scheffler (13) and Smith (14). The specific activity of ODC was deter- mined by measuring the release of I4CO2 from DL-[1- 14C] ornithine hydrochloride (, Amersham, 58 mCi/mmol). The enzyme reaction was performed in a 16 mm (ID) borosilicate test tube capped with a double- seal rubber stopper (Kontes, K-882310) penetrated by a plastic cente
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
