A general method for modifying eukaryotic genes by site-specific mutagenesis and subsequent expression in mammalian cells was developed to study the relation between structure and function of the proteolytic enzyme trypsin. Glycine residues at positions 216 and 226 in the binding cavity of trypsin were replaced by alanine residues, resulting in three trypsin mutants. Computer graphic analysis suggested that these substitutions would differentially affect arginine and lysine substrate binding of the enzyme. Although the mutant enzymes were reduced in catalytic rate, they showed enhanced substrate specificity relative to the native enzyme. This increased specificity was achieved by the unexpected differential effects on the catalytic activity toward arginine and lysine substrates. Mutants containing alanine at position 226 exhibited an altered conformation that may be converted to a trypsin-like structure upon binding of a substrate analog.

A cDNA encoding rat cationic trypsinogen has been isolated by immunoscreening from a rat pancreas cDNA library. The protein encoded by this cDNA is highly basic and contains all of the structural features observed in trypsinogens. The amino acid sequence of rat cationic trypsinogen is 75% and 77% homologous to the two anionic rat trypsinogens. The homology of rat cationic trypsinogen to these anionic trypsinogens is lower than its homology to other mammalian cationic trypsinogens, suggesting that anionic and cationic trypsins probably diverged prior to the divergence of rodents and ungulates. The most unusual feature of this trypsinogen is the presence of an activation peptide containing five aspartic acid residues, in contrast to all other reported trypsinogen activation peptides which contain four acidic amino acid residues. Comparisons of cationic and anionic trypsins reveal that the majority of the charge changes occur in the C-terminal portion of the protein, which forms the substrate binding site. Several regions of conserved charge differences between cationic and anionic trypsins have been identified in this region, which may influence the rate of hydrolysis of protein substrates.

Population geneticists have often determined the fitness differences that account for the dynamics of naturally occurring genetic polymorphisms. However, to understand causal aspects of evolutionary processes requires, in addition, investigation of the physiological and molecular structural differences underlying adaptively significant genetic polymorphisms. The characteristics of the alcohol dehydrogenase gene-enzyme system in Drosophila melanogaster make it well suited for this kind of study. Natural populations of this species are polymorphic for two electrophoretically detectable variants, ADHF and ADHS, of the enzyme. Structural studies reported here reveal that the two variants differ by (at least) a single amino acid replacement, threonine in ADHF for lysine in ADHS.Genetic polymorphisms are of great interest to evolutionists because they permit investigation of the adaptive basis and of the dynamics of the processes of genetic change underlying adaptive evolution. At a first level of investigation, population geneticists are concerned with ascertaining whether or not alternative genotypes differ in fitness; fitness differences may lead to the evolutionary replacement of one allele for another but may also lead to equilibrium polymorphic situations with two or more alleles maintained at certain frequencies. The causal study of genetic evolution requires, moreover, investigation of the functional (physiological) and biochemical (molecular) bases of fitness differences. It is remarkable that more than a century after Darwin (and more than four decades after the birth of experimental population genetics), we know the physiological and biochemical bases of very few polymorphisms. The sickle-cell polymorphism in regions where malaria is rife represents the most familiar example. An urgent need exists for ascertaining the physiological and biochemical bases of the pervasive polymorphisms found in nature.A polymorphism that has been much investigated in recent years involves the Adh locus and its gene product, alcohol dehydrogenase (ADH; alcohol:NAD+ oxidoreductase, EC 1.1.1.1), in Drosophila melanogaster (1). Two electrophoretically distinguishable forms of the enzyme, one ("fast," ADHF) migrating farther than the other ("slow," ADHS), are found in natural populations throughout the world. A rare variant, termed "ultrafast" (ADHUF), has been found in a Spanish population (2) and a variant (ADHD) with the same mobility as ADHUF has been obtained through ethyl methanesulfonate treatment (3).The adaptive basis of the ADH polymorphism has been extensively studied. Flies possessing the ADHF (or ADHUF) form of the enzyme exhibit greater tolerance of environmental alcohol than do flies having the ADHS form (4-7). The physiological basis of this difference in alcohol tolerance has beenThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. (8). The difference in ADH activity between the selected...

Transketolase (EC 2.2.1.1) is the enzyme that, together with aldolase, forms a reversible link between the glycolytic and pentose phosphate pathways. We have cloned and sequenced the transketolase gene from yeast (Saccharomyces cerevisiae). This is the first transketolase gene of the pentose phosphate shunt to be sequenced from any source. The molecular mass of the proposed translated protein is 73,976 daltons, in good agreement with the observed molecular mass of about 75,000 daltons. The 5'-nontranslated region of the gene is similar to other yeast genes. There is no evidence of 5'-splice junctions or branch points in the sequence. The 3'-nontranslated region contains the polyadenylation signal (AATAAA), 80 base pairs downstream from the termination codon. A high degree of homology is found between yeast transketolase and dihydroxyacetone synthase (formaldehyde transketolase) from the yeast Hansenula polymorpha. The overall sequence identity between these two proteins is 37%, with four regions of much greater similarity. The regions from amino acid residues 98-131, 157-182, 410-433, and 474-489 have sequence identities of 74%, 66%, 83%, and 82%, respectively. One of these regions (157-182) includes a possible thiamin pyrophosphate (TPP) binding domain, and another (410-433) may contain the catalytic domain.

Although protease E was isolated from human pancreas over 10 years ago [Mallory, P. A., & Travis, J. (1975) Biochemistry 14, 722-729], its amino acid sequence and relationship to the elastases have not been established. We report the isolation of a cDNA clone for human pancreatic protease E and determination of the nucleic acid sequence coding for the protein. The deduced amino acid sequence contains all of the features common to serine proteases. The substrate binding region is highly homologous to those of porcine and rat elastases 1, explaining the similar specificity for alanine reported for protease E and these elastases. However, the amino acid sequence outside the substrate binding region is less than 50% conserved, and there is a striking difference in the overall net charge for protease E (6-) and elastases 1 (8+). These findings confirm that protease E is a new member of the serine protease family. We have attempted to identify amino acid residues important for the interaction between elastases and elastin by examining the amino acid sequence differences between elastases and protease E. In addition to the large number of surface charge changes which are outside the substrate binding region, there are several changes which might be crucial for elastolysis: Leu-73/Arg-73; Arg-217A/Ala-217A; Arg-65A/Gln-65A; and the presence of two new cysteine residues (Cys-98 and Cys-99B) which computer modeling studies predict could form a new disulfide bond, not previously observed for serine proteases. We also present evidence which suggests that human pancreas does not synthesize a basic, alanine-specific elastase similar to porcine elastase 1.