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Department of Chemistry, University of Calicut, Kerala-673 635 Manuscript received 16 October 1995, relined 17 April 1996. accepted 19 June 1996 Synthesis and Characterisation of Cobalt-, Nickel-, Copper- and Zinc(II) Complexes of Morin.

Department of Chemistry. University of Calicut, Kerala-673 635 Manuscript received 29 December 1995, accepted 14 May 1996 Binuclear Metal Chelates of 1-(2-Hydroxyphenyl)-3-phenyl-1 ,3-propanedione.

Salivary alpha-amylase, a major component of human saliva, plays a role in the initial digestion of starch and may be involved in the colonization of bacteria involved in early dental plaque formation. The three-dimensional atomic structure of salivary amylase has been determined to understand the structure-function relationships of this enzyme. This structure was refined to an R value of 18.4% with 496 amino-acid residues, one calcium ion, one chloride ion and 170 water molecules. Salivary amylase folds into a multidomain structure consisting of three domains, A, B and C. Domain A has a (beta/alpha)(8-) barrel structure, domain B has no definite topology and domain C has a Greek-key barrel structure. The Ca(2+) ion is bound to Asnl00, Arg158, Asp167, His201 and three water molecules. The Cl(-) ion is bound to Arg195, Asn298 and Arg337 and one water molecule. The highly mobile glycine-rich loop 304-310 may act as a gateway for substrate binding and be involved in a 'trap-release' mechanism in the hydrolysis of substrates. Strategic placement of calcium and chloride ions, as well as histidine and tryptophan residues may play a role in differentiating between the glycone and aglycone ends of the polysaccharide substrates. Salivary amylase also possesses a suitable site for binding to enamel surfaces and provides potential sites for the binding of bacterial adhesins.