Emil L. Smith

Anomalous cleavage of aspartyl-proline peptide bonds during amino acid sequence determinations

Abstract Aspartyl-proline peptide bonds have been found to be hydrolyzed during exposure to low pH values under conditions where other aspartyl bonds are stable. The mechanism of this hydrolytic reaction is concluded to proceed via intramolecular catalysis by carboxylate anion displacement of the protonated nitrogen of the peptide bond. The enhanced rate with proline as compared to other amino acids is undoubtedly due to the greater basicity of the proline nitrogen.

Structural and Functional Aspects of Cytochrome c in Relation to Evolution

Publisher Summary The protein cytochrome c constitutes a set of evolutionarily homologous structures. With the exception of many microorganisms, the mammalian type of cytochrome c is universally present in species for which oxygen serves as the terminal oxidant of metabolism. This class of protein has been utilized since the beginning of aerobic life on earth. Its phylogenetic antiquity assures that cytochrome c is a suitable object for the study of the relationships, if any, between the evolution of species and that of a particular protein. This chapter discusses the features of cytochrome c that remain constant in evolution and their use in inferring the evolutionary homology of these proteins. It further discusses the variable features and the quantitative aspects of phylogeny exhibited by cytochrome c. The chapter also presents some evolutionary aspects of structure–function relations in cytochrome c.

Some properties of soybean lipoxygenase

Abstract Commercial soybean lipoxygenase (EC 1.99.2.1) was purified by ammonium sulfate fractionation, gel filtration on Sephadex G-150, and chromatography on DEAE-cellulose. The purified protein was essentially homogeneous as judged by acrylamide gel electrophoresis and ultracentrifugation. The molecular weight is 108,000 as determined by the sedimentation-equilibrium method. The amino acid composition was determined, and it was shown that the protein contains four residues of free sulfhydryl groups and four residues of half-cystine per molecule. Treatment of the protein with guanidine hydrochloride or sodium dodecyl sulfate produces dissociation. Present evidence indicates that the protein is composed of two subunits of 54,000 molecular weight.

Calf thymus histone III: Sequences of the amino- and carboxyl-terminal regions and of the regions containing lysyl residues modified by acetylation and methylation

Abstract Sequence studies on the tryptic peptides from maleylated calf thymus histone III showed one site of e-N-methylation in the sequence Arg-Lys (CH 3 ) 0–2 -Ala-Ser-Pro-Ala-Thr-Gly-Gly-Val-Lys-Lys-Pro-His-Arg, and two sites of e-N-acetylation in the sequences Arg-Lys-Ser-Thr-Gly-Gly-Lys(Ac)-Ala-Pro-Arg and Arg-Lys-Gin-Leu Ala-Thr-Lys(Ac)-Ala-Ala-Arg. The NH 2 -terminal sequence of histone III is probably Ala-Arg,and the sequence of 20 residues at the CDOR-terminus has been established. There is little or no similarity when these regions of calf thymus histones III and IV are compared.

Some Structure-Function Relationships in the Subtilisins

Publisher Summary This chapter discusses some structure-function relationships in the subtilisins. It is evident that considerable variation in primary sequence exists among the subtilisins, although these form a homologous family of enzymes. One shall not be concerned with problems of bacterial taxonomy, although some of these enzymes may be produced by different species and, perhaps, even by different genera, but shall use the name subtilisin in the broadest sense. The residues near the active serine residue may have little influence on the reaction mechanism, in determining the reactivity of the serine hydroxyl group or in determining the specificity of the enzyme. However, sequences may be of taxonomic value in classifying the various types of enzymes. Although the reactive serine residue in the subtilisins is in an invariant sequence, this is not the case for the reactive histidine. The residue on the amino-terminal side of histidine 64 is glycine for the Carlsberg enzyme and serine for BPN’. It is tempting to assume that this single amino acid replacement may account in part for the absolute greater activity of subtilisin Carlsberg and some of the small differences in specificity exhibited by two enzymes.

Alternative substrates for glutamate dehydrogenases

Summary The amide group of glutamine functions as a nitrogen donor in the reactions catalyzed by both the NADP-specific glutamate dehydrogenase of Neurospora crassa and the bovine liver enzyme, but not by the NAD-specific Neurospora enzyme. Asparagine serves as nitrogen source only for the NADP-specific Neurospora dehydrogenase. The optimum for utilization of the amide substrates is at pH 8.4 with both enzymes as contrasted to the value of pH 7.6 to 7.8 obtained with ammonia as the source of nitrogen. The maximal rate of reaction with ammonia is 2.5 times greater than that with glutamine and 10 times greater than that with asparagine at the respective pH optima. Acetamide does not serve as a source of nitrogen for either of these two enzymes.

Amino acid sequences of proteins--the beginnings.

T H E EARLY HISTORY of the study of the amino acid sequences of proteins can, perhaps, be more readily appreciated if we can recall the general state of protein chemistry immediately prior to this time. The extraordinary burst of activity in the investigation of amino acid sequences resulted from the confluence of both conceptual developments and experimental methods. Although some of these contributions will be discussed in detail by others a t this meeting, it seems useful to remind ourselves of the situation at that time, although only brief attention can be devoted to some of the factors that led to the subsequent rapid developments. Of greatest importance was the increasing evidence in the period between 1925 and 1935 that many important biological activities were due to specific proteins, including enzymes, antibodies, oxygen carriers, and some hormones. Although there was considerable information to support these views much earlier, it was not until these concepts were put on a firm experimental basis that protein chemistry aroused wide interest among biologists and chemists. During this same period, it had been fairly well established that the major covalent linkage between amino acid residues in proteins was the peptide bond. Concurrently, it was recognized that most, if not all, of the amino acids commonly found in proteins were known,l with glutamine, asparagine, and threonine being the last to be firmly established as general constituents of proteins2; nevertheless, in no instance was there available a complete accounting of the amino acid composition of a p r ~ t e i n . ~