Calcium/calmodulin-dependent protein kinase II (CaMPK-II) is a key regulatory enzyme in living cells. Modulation of its activity, therefore, could have a major impact on many cellular processes. We found that Zn 2ϩ has multiple functional effects on CaMPK-II. Zn 2ϩ generated a Ca 2ϩ /CaM-independent activity that correlated with the autophosphorylation of Thr 286 , inhibited Ca 2ϩ / CaM binding that correlated with the autophosphorylation of Thr 306 , and inhibited CaMPK-II activity at high concentrations that correlated with the autophosphorylation of Ser 279 . The relative level of autophosphorylation of these three sites was dependent on the concentration of zinc used. The autophosphorylation of at least these three sites, together with Zn 2ϩ binding, generated an increased mobility form of CaMPK-II on sodium dodecyl sulfate gels. Overall, autophosphorylation induced by Zn 2ϩ converts CaMPK-II into a different form than the binding of Ca 2ϩ /CaM. In certain nerve terminals, where Zn 2ϩ has been shown to play a neuromodulatory role and is present in high concentrations, Zn 2ϩ may turn CaMPK-II into a form that would be unable to respond to calcium signals. Key Words: Zinc-Calcium/calmodulin-Calcium/calmodulin-stimulated protein kinase II-Autonomous activity-Autophosphorylation-Phosphorylation site analysis.

;Influxes of glucose, fructose and sucrose were characterised for coat cells of developing seeds of Phaseolus vulgaris L. and Vicia faba L. by monitoring uptake of [14 C]sugars into excised seed-coat halves and two different protoplast populations derived from seed coats. Sugar influxes by the two populations of protoplasts were similar for each sugar species [sucrose > (fructose » glucose)] and hexoses competed with sucrose. Concentration-dependent influxes of all three sugars by excised seed coats could be described by a simple directly proportional relationship between concentration ([S]) and uptake rate (v) in the physiological range of sugar concentrations (v » A.[S]). Alternatively, with the exception of fructose influx by Vicia, all could be fitted to a Michaelis-Menten relationship, as could sucrose uptake by Vicia protoplasts. Apparent K m values were high (» 100-500 mM) compared with those reported for other systems. Sucrose transport was distinct from glucose and fructose transport in both species. Sugar influx was decreased by p-chloromercuribenzenesulfonic acid, carbonylcyanide m-chlorophenylhydrazone and erythrosin B. These responses are consistent with sugar/H + symport acting to retrieve photoassimilates leaked to the apoplasm during post-sieve element transport within seed coats.

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