X-ray diffraction analysis (at 2.1-A resolution) of an acid alpha-amylase from Aspergillus niger allowed a detailed description of the stereochemistry of the calcium-binding sites. The primary site (which is essential in maintaining proper folding around the active site) contains a tightly bound Ca2+ with an unusually high number of eight ligands (O delta 1 and O delta 2 of Asp175, O delta of Asn121, main-chain carbonyl oxygens of Glu162 and Glu210, and three water molecules). A secondary binding site was identified at the bottom of the substrate binding cleft; it involves the residues presumed to play a catalytic role (Asp206 and Glu230). This explains the inhibitory effect of calcium observed at higher concentrations. Neutral Aspergillus oryzae (TAKA) alpha-amylase was also refined in a new crystal at 2.1-A resolution. The structure of this homologous (over 80%) enzyme and additional kinetic studies support all the structural conclusions regarding both calcium-binding sites.

SummaryInsulin-dependent diabetes mellitus (IDDM) is associated with autoreactivity against GAD but the diagnostic sensitivity (positivity in disease) and specificity (negativity in health) of isoform-specific GAD antibodies have yet to be defined in assay systems suitable for screening large number of samples. One set of IDDM patient (n = 10) and control (n = 50) standard sera were used to develop quantitative antibody assays with in vitro synthesized recombinant 35S-methionine-labelled GAD65 and GAD67, respectively, and protein A-Sepharose to separate free from antibody-bound ligand. Binding levels were not normally distributed (p < 0.0001) and therefore, the diagnostic accuracy of GAD antibodies was analysed by the ROC plots in population-based, consecutively-diagnosed, recent onset, 0-14year-old patients (n = 105), and matched, healthy control subjects (n = 157). The ROC plots showed that the diagnostic sensitivity of GAD65 antibodies was 77 % and the specificity 92 % compared with 8 % and 98 %, respectively for GAD67 antibodies. In the IDDM sera, GAD65 and GAD67 antibodies were concordant in 7% (6 of 81) and GAD65 antibodies and ICA in 89 % (72 of 81) without a correlation between the autoantibody levels. Autoantibodies to recombinant human islet GAD65 are specific and sensitive markers for childhood IDDM in this immunoassay with in vitro synthesized 35S-methioninelabelled recombinant GAD. [Diabetologia (1994) Abbreviations: IDDM, insulin-dependent diabetes mellitus; GAD, glutamic acid decarboxylase; ROC, receiver-operating characteristic; ICA, islet cell antibodies; JDF, Juvenile Diabetes Foundation 10p11.3-p12 [7]. GAD65 shows 65 % amino acid identity with GAD67, the isoform coded for by the GAD1 gene on chromosome 2q31 [7][8][9]. The molecular cloning of full-length human islet GAD65 [7] and rat islet GAD67 [10] cDNA has made it possible to demonstrate autoreactivity in diabetes to the recombinant proteins in both eukaryotic [11,12] and bacterial [13] expression systems. GAD65 (but not GAD67) is expressed in human islets [11,14], however, variable reactivity of patient sera has been reported [12,13,[15][16][17][18][19]. GAD65 specificity of IDDM sera was first demonstrated in our immunoprecipitation assay with recombinant GAD expressed in transfected cells [12] and recently confirmed in other assays with recombinant antigens [18,20]. The use of different assay systems and species-specific GAD65 and GAD67 may explain the lower frequency of GAD67 antibodies in these compared to previous reports [13,16]. We now report the

The primary structure ofglucoamylase G1 (EC 3.2.1.3) from Aspergillus niger has been determined. Fragments of GI were obtained by cleavage with either cyanogen bromide, hydroxylamine, or S. aureus V8 protease. The resulting peptides were separated using ion exchange chromatography on DEAE-Sephacel, gel filtration, and affinity chromatography on Con A-Sepharose. Secondary fragments were generated by cleavage with either o-iodosobenzoic acid or BNPS-skatole as well as by digestion with S. aureus V8 protease, trypsin, and endoproteinase Lys-C. These peptides were purified by the procedures mentioned above and by reverse phase HPLC. The present fragments were amino acid sequenced and this permitted, in combination with the tryptic peptides (Carlsberg Res. Commun. 48, 517-527 (1983)), identification of 574 of the 614 amino acid residues in Gl. Sequencing of glucoamylase Gl cDNA, constructed from A. niger total mRNA, enabled deduction of the sequence of the remaining 40 amino acid residues localized to 6 short stretches. From the alignment of the fragments the complete primary structure of the enzyme was established. The amino acid sequence corresponds to a molecular weight of the polypeptide moiety of 65,424. Including both hexosamine and neutral carbohydrate contents the molecular weight of the present sample of G1 was calculated to be about 82,000.The majority of the carbohydrate of Gl is found in a highly glycosylated region of 70 amino acid residues which comprises about 35 O-glycosyl serine and threonine residues. This region ends approximately 100 residues from the C-terminus of the enzyme. Two N-glycosylated positions were found in the central part of the polypeptide chain. The molecule contains 9 half-cystine residues. No homology is apparent between the sequence of glycoamylase and various at-amylases.Abbreviations: BNPS-skatole = 2-(2-nitrophenylsulfenyl)-3-methyl-3'-bromoindolenine; ca = citraconyl; Con A = concanavalin A; DFP = diisopropylfluorophosphate; DPCC = diphenylcarbamyl chloride; EDTA = ethylenediaminetetraacetic acid, disodium salt; Hepes = N-2-hydroxyethyl piperazine-N'-2-ethanesulfonic acid; Nemac = N-ethylmorpholine acetate; HPLC = high pressure liquid chromatography; PTH = phenylthiohydantoin; SDS-PAGE = polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate; 2-pe = 2-pyridylethyl; G I designates the larger and G2 the smaller of the forms ofglucoamylase from A. niger (44).

Insulin-dependent diabetes mellitus (IDDM) is associated with autoreactivity against GAD but the diagnostic sensitivity (positivity in disease) and specificity (negativity in health) of isoform-specific GAD antibodies have yet to be defined in assay systems suitable for screening large number of samples. One set of IDDM patient (n = 10) and control (n = 50) standard sera were used to develop quantitative antibody assays with in vitro synthesized recombinant 35S-methionine-labelled GAD65 and GAD67, respectively, and protein A-Sepharose to separate free from antibody-bound ligand. Binding levels were not normally distributed (p < 0.0001) and therefore, the diagnostic accuracy of GAD antibodies was analysed by the ROC plots in population-based, consecutively-diagnosed, recent onset, 0-14 year-old patients (n = 105), and matched, healthy control subjects (n = 157). The ROC plots showed that the diagnostic sensitivity of GAD65 antibodies was 77% and the specificity 92% compared with 8% and 98%, respectively for GAD67 antibodies. In the IDDM sera, GAD65 and GAD67 antibodies were concordant in 7% (6 of 81) and GAD65 antibodies and ICA in 89% (72 of 81) without a correlation between the autoantibody levels. Autoantibodies to recombinant human islet GAD65 are specific and sensitive markers for childhood IDDM in this immunoassay with in vitro synthesized 35S-methionine-labelled recombinant GAD.

Typically pancreatic lipases are characterized by the following properties: (1) they are activated by lipid/water interfaces (interfacial activation), (2) they are inhibited by bile salts but reactivated by colipase (a small activator protein), and (3) they do not hydrolyze significantly phospholipids. A cDNA clone encoding a guinea pig pancreatic (phospho)lipase (GPL) has been sequenced and expressed. The enzyme (recombinant as well as native) differs from other pancreatic lipases in that (1) it is not interfacially activated, (2) its activity is unaffected by the presence of bile salts and/or colipase using tributyrin as substrate, and (3) it exhibits equally phospholipase A1 and lipase activities. The amino acid sequence of GPL is highly homologous to that of other known pancreatic lipases, with the exception of a deletion in the so-called lid domain that regulates access to the active centers of other lipases. We propose that this deletion is directly responsible for the anomalous behavior of this enzyme. Thus GPL challenges the classical distinction between lipases, esterases, and phospholipases.