The partial removal of tightly bound Ca²⁺ from dialysed neem (Azadirachta indica) gum, resulted in the release of a basic protein from a highly anionic polysaccharide-protein complex as evidenced by chromatographic studies on TEAE-cellulose. Complete removal of Ca²⁺ caused, in addition, the release of a minor heteropolysaccharide which was found in association with the basic protein. These processes were reversed on the addition of Ca²⁺. The gum, in addition, contained a protein-rich component accounting for 35% protein and 7.5% total carbohydrate. This component behaved as a distinct entity during ion-exchange chromatography of the native gum solutions, or which were either partially or completely depleted of bound Ca²⁺.

Aspartokinase fromMicrococcus glutamicus AEC RN-13-6/1 [a homoserine requiring, S-(2-aminoethyl)-L-cysteine resistant, lysine producing strain] was purified 71 fold. The partially purified enzyme was inhibited by L-lysine. L-threonine, L-methionine, L-isoleucine, L-valine and L-phenylalanine activated the enzyme and reversed the inhibition by L-lysine. Aspartokinase activity was not derepressed by growth-limiting concentrations of L-threonine and/or L-methionine. It was not repressed by an excess of L-lysine (20 mM) and/or L-isoleucine (15.3 mM). The degree of activation or inhibition by amino acids was dependant on the composition of the growth medium. This observation is in contrast with the enzyme from the original (non-lysine-producing) strain which was inhibited by lysine or threonine and in a concerted manner by threonine plus lysine.

Diaminopimelate decarboxylase (EC 4.1.1.20) ofMicrococcus glutamicus ATCC 13059 was purified to homogeneity. The enzyme had an apparent molecular weight of 191,000 as determined by gel filtration on Sephadex G-200. At protein concentrations of 20 and 10 μg per ml and in the absence of pyridoxal-5′-phosphate, it dissociated into a species of molecular weight 94,000. The polypeptide chain molecular weight as determined by sodium dodecyl sulphate Polyacrylamide gel electrophoresis was 100,000. TheK_m formeso diaminopimelate was 0.5 mM and that for pyridoxal-5′-phosphate was 0.6 μI. Sulphydryl groups and pyridoxal-5′-phosphate were essential for activity and stability. The enzyme was inhibited significantly by L-lysine and DL-aspartic β-semialdehyde.

Glucoamylase II (EC 3.2.1.3) fromAspergillus niger has 31 % α-helix, 36 %Β- structure and rest aperiodic structure at pH 4.8 as analysed by the method of Provencher and Glockner (1981,Biochemistry, 20,33). In the near ultra-violet circular dichroism spectrum the enzyme exhibits peaks at 304, 289, 282 and 257 nm and troughs at 285, 277 and 265 nm respectively. The enzyme activity and structure showed greater stability at pH 4.8 than at pH 7.0, were highly sensitive to alkaline pH but less sensitive to acid pH values. The enzyme retained most of its catalytic activity and structure even on partial removal of carbohydrate moieties by periodate treatment but was less stable at higher temperatures and storage at 30‡C. Reduction of the periodate treated enzyme did not reverse the loss of stability. Binding of the synthetic substrate,p-nitrophenyl-α-D-glucoside, perturbed the environment around aromatic amino acids and caused a decrease in the ordered structure.

The purification and properties of glucoamylase (α-l,4-glucan glucohydrolase, EC 3.2.1.3) from different fungal sources have been compared. The studies on the conformation and activity of the native enzyme at a function of pH, temperature, substrate concentration and the effect of denaturants and on the role of carbohydrate moiety on structure and stability have been reviewed. The chemical modification of the active centre, binding kinetics of the substrate and active site and the mechanism of action have been summarized. They differ in their fine structure as revealed by their near ultra-violet circular dichroism spectra and contain 30–35 % α-helix, 24–36 %Β-structure and the rest aperiodic structure. The activity of the enzyme is very sensitive to the environment around aromatic aminoacid residues.

The glucoamylases are glycoprotein in nature, differ in their content and nature of carbohydrate from different sources. The carbohydrate moiety plays an important role in stabilising the native conformation of the enzyme and is not involved in activity and antigenecity.

At the active site of the enzyme, two tryptophan and two carboxyl (glutamate or aspartate) groups are present. It is likely that the histidine and tyrosine residues which are present away from the active site are involved in binding of the substrate. There seems to be seven subsites which are involved in binding of the substrate and the catalytic site is situated in between 1 and 2 subsites. In breaking of α-1,4-, α-1,3-, and α-l,6-bonds only one active centre is involved.

Studies on the immobilization of either glucoamylase alone or as a part of a multienzyme system have been reviewed briefly

The histidine, tyrosine, tryPtoPhan and carboxyl grouPs in the enzyme glucoamylase fromAsPergillus Candidus andRhizoPus sPecies were modified using grouP sPecific reagents. Treatment of the enzyme with diethylPyrocarbonate resulted in the modification of 0.3 and 1 histidine residues with only a slight loss in activity (10% and 35%) of glucoamylase fromAsPergillus candidus andRhizoPus sPecies resPectively. Modification of tyrosine either by N-acetylimidazole or [I¹²⁵]-leads to a Partial loss of activity. Under denaturing conditions, maltose did not helP in Protecting the enzyme against tyrosine modification or inactivation. Treatment with 2-Hydroxy-5-nitro benzyl bromide in the Presence of urea, Photooxidation at PH 9.0, N-bromosuccinamide at PH 4.8 resulted in a comPlete loss of activity. However, the results of exPeriments in the Presence of maltose and at PH 4.8 Photooxidation and N-bromosuccinamide treatment suggested the Presence of two tryPtoPhan residues at the active site. There was a comPlete loss of enzyme activity when 10 and 28 carboxyl grouPs fromAsPergillus candidus andRhizoPus, resPectively were modified. Modification in the Presence of substrate maltose, showed at least two carboxyl grouPs were Present at the active site of enzyme and that only one active center seems to be involved in breaking ally 3 tyPes of α-glucosidic linkages namely α-1, 4, α-1, 6 and α-l, 3.