摘要:

The amino acid sequence of the cyanogen bromide peptide (peptide B) containing the putative essential tyrosine residue in Bacillus amyloliquefaciens alpha‐amylase (EC 3.2.1.1.) was determined. It is composed of 73 amino acids and the “active” tyrosine residue is the N‐terminus of the peptide. Upon iodination of the whole enzyme by means of a lactoperoxidase‐catalyzed reaction, a minimum of eight tyrosine residues are iodinated. Four of these belong to peptide B. Among the cyanogen bromide peptides, B is the most readily iodinated one. Hence, it is predicted that peptide B is an exposed segment of the amylase

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb01972.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The isolation and characterization of the products formed during the irreversible thermal denaturation of enzyme RNAase‐A are described. RNAase‐A, when maintained in aqueous solution at pH 7.0 and 70° for 2 h, gives soluble products which have been fractionated by gel filtration on Sephadex G‐75 into four components. These components are designated RNAase‐At1, RNAase‐At2, RNAase‐At3and RNAase‐At4according to the order of their elution from Sephadex G‐75. RNAase‐At4shows the same specific activity towards yeast RNA as native RNAase‐A and is virtually indistinguishable from it by the physical methods employed. However, chromatography on CM‐cellulose separates it into three components that show the same u.v. spectra and specific activity towards yeast RNA as native RNAase‐A. RNAase‐At1, RNAase‐At2and RNAase‐At3are all structurally altered derivatives of RNAase‐A and they exhibit low specific activity (5–10%) towards yeast RNA. In the presence of added S‐protein, all these derivatives show greatly enhanced enzymic activity. RNAase‐At1and RNAase‐At2are polymers, covalently crosslinked by intermolecular disulfide bridges; whereas RNAase‐At3is a monomer. Physical studies such as1H‐n.m.r., sedimentation analysis, u.v. absorption spectra and CD spectra reveal that RNAase‐At3is a unfolded derivative of RNAase‐A. However, it is seen to possess sufficient residual structure which gives rise

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb01973.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Four stereoisomers (I‐LL, I‐LD, I‐DL and I‐DD) of a cyclic depsidipeptide (I) containing a tryptophan and a 2‐hydroxy‐4‐methylpentanoic acid residue were synthesized, and their taste and chymotryptic susceptibility were examined. Compound I‐LL is a depsipeptide analog of a bitter principle BP‐II, cyclo(‐L‐Trp‐L‐Leu‐), obtained from casein hydrolyzate. All of the four stereoisomers of I are strongly bitter to taste. Another depsipeptide analog, L‐aspartyl‐L‐2‐hydroxy‐3‐phenylpropanoic acid methyl ester, of the sweet H‐L‐Asp‐L‐Phe‐ OMe showed bitter taste instead of sweet. Chymotrypsin hydrolyzed I‐LL and I

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb01974.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Circular dichroism spectra (CD) of an active fraction of antifreeze glycoprotein (AFGP) and of a lower molecular weight fraction which is less active are found to be similar in the wavelength range 170–230 nm. The contribution of the disaccharide side chain chromophores to the CD spectra of the glycoprotein is estimated from spectra of model oligosaccharides having similar structures. Comparison of the CD spectra of the peptide portion of AFGP to those of established model polypeptides suggests a 3‐fold left‐handed helix of the collagen type as the most likely conformation of the peptide. In the proposed model, the disaccharide moieties attached to every third residue are in identical environments. Furthermore, proline residues which are found in the less active fraction can be accommodated in this helical structure, consistent with the observed similarity of the spectra of the two frac

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb01975.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY