RELATIONSHIPS BETWEEN GDH AND LDH ACTIVITY IN THEIR RESPECTIVE NADH-DEPENDENT REACTIONS IN THE CHELIPED MUSCLE OF THE CRAB, CANCER-PAGURUS

1. The presence of an interfering dehydrogenase, when measuring GDH activity in crude extract of crab muscle, led us to study a possible interference of LDH in the enzyme assay, through competition for NADH. 2. In the cheliped muscle of C. pagurus, LDH activity was one order of magnitude higher than GDH activity. 3. LDH activity was particularly low (28 +/- 5.1 IU/g muscle) during early postmoult when the highest GDH activity (3.92 +/- 0.17) was observed. On the other hand, LDH activity was much higher in carpus/merus muscle (100 +/- 7.27 IU/g muscle) than in propodus muscle (52 +/- 2.2), whereas the reverse occurred for GDH activity. 4. The activity of the interfering dehydrogenase (CA) regularly made up 1% of LDH activity, in spite of changes in LDH activity level. CA was positively correlated to LDH activity and negatively correlated to GDH activity. 5. The linear and negative correlation between GDH and LDH suggested that in vivo GDH activity was very likely modulated by the activity level of LDH.