Aspartic Acid Proteases: A subclass of peptide hydrolases that depend on an ASPARTIC ACID residue for their activity.Aspartic Acid: One of the non-essential amino acids commonly occurring in the L-form. It is found in animals and plants, especially in sugar cane and sugar beets. It may be a neurotransmitter.Pepstatins: N-acylated oligopeptides isolated from culture filtrates of Actinomycetes, which act specifically to inhibit acid proteases such as pepsin and renin.Aspartic Acid Endopeptidases: A sub-subclass of endopeptidases that depend on an ASPARTIC ACID residue for their activity.Protease Inhibitors: Compounds which inhibit or antagonize biosynthesis or actions of proteases (ENDOPEPTIDASES).Endopeptidases: A subclass of PEPTIDE HYDROLASES that catalyze the internal cleavage of PEPTIDES or PROTEINS.Norleucine: An unnatural amino acid that is used experimentally to study protein structure and function. It is structurally similar to METHIONINE, however it does not contain SULFUR.Peptide Hydrolases: Hydrolases that specifically cleave the peptide bonds found in PROTEINS and PEPTIDES. Examples of sub-subclasses for this group include EXOPEPTIDASES and ENDOPEPTIDASES.Rhizopus: A genus of zygomycetous fungi of the family Mucoraceae, order MUCORALES, a common saprophyte and facultative parasite of mature fruits and vegetables. It may cause cerebral mycoses in diabetes and cutaneous infection in severely burned patients.Mucor: A genus of zygomycetous fungi of the family Mucoraceae, order Mucorales. It is primarily saprophytic, but may cause MUCORMYCOSIS in man from spores germinating in the lungs.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Cathepsin D: An intracellular proteinase found in a variety of tissue. It has specificity similar to but narrower than that of pepsin A. The enzyme is involved in catabolism of cartilage and connective tissue. EC 126.96.36.199. (Formerly EC 188.8.131.52).Aspergillus oryzae: An imperfect fungus present on most agricultural seeds and often responsible for the spoilage of seeds in bulk storage. It is also used in the production of fermented food or drink, especially in Japan.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Pepsin A: Formed from pig pepsinogen by cleavage of one peptide bond. The enzyme is a single polypeptide chain and is inhibited by methyl 2-diaazoacetamidohexanoate. It cleaves peptides preferentially at the carbonyl linkages of phenylalanine or leucine and acts as the principal digestive enzyme of gastric juice.Hydrogen-Ion Concentration: The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH = log 1/2[1/(H+)], where (H+) is the hydrogen ion concentration in gram equivalents per liter of solution. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Cathepsin E: An aspartic endopeptidase that is similar in structure to CATHEPSIN D. It is found primarily in the cells of the immune system where it may play a role in processing of CELL SURFACE ANTIGENS.Chymosin: The predominant milk-clotting enzyme from the true stomach or abomasum of the suckling calf. It is secreted as an inactive precursor called prorennin and converted in the acid environment of the stomach to the active enzyme. EC 184.108.40.206.Mitosporic Fungi: A large and heterogenous group of fungi whose common characteristic is the absence of a sexual state. Many of the pathogenic fungi in humans belong to this group.HIV Protease: Enzyme of the human immunodeficiency virus that is required for post-translational cleavage of gag and gag-pol precursor polyproteins into functional products needed for viral assembly. HIV protease is an aspartic protease encoded by the amino terminus of the pol gene.Amino Acids: Organic compounds that generally contain an amino (-NH2) and a carboxyl (-COOH) group. Twenty alpha-amino acids are the subunits which are polymerized to form proteins.Cathepsins: A group of lysosomal proteinases or endopeptidases found in aqueous extracts of a variety of animal tissues. They function optimally within an acidic pH range. The cathepsins occur as a variety of enzyme subtypes including SERINE PROTEASES; ASPARTIC PROTEINASES; and CYSTEINE PROTEASES.Aspergillus niger: An imperfect fungus causing smut or black mold of several fruits, vegetables, etc.Saccharomycopsis: Yeast-like ascomycetous fungi of the family Saccharomycopsidaceae, order SACCHAROMYCETALES, isolated from the stomach of rabbits and some other animals.NitrophenolsPepsinogens: Proenzymes secreted by chief cells, mucous neck cells, and pyloric gland cells, which are converted into pepsin in the presence of gastric acid or pepsin itself. (Dorland, 28th ed) In humans there are 2 related pepsinogen systems: PEPSINOGEN A (formerly pepsinogen I or pepsinogen) and PEPSINOGEN C (formerly pepsinogen II or progastricsin). Pepsinogen B is the name of a pepsinogen from pigs.Serine Endopeptidases: Any member of the group of ENDOPEPTIDASES containing at the active site a serine residue involved in catalysis.Binding Sites: The parts of a macromolecule that directly participate in its specific combination with another molecule.Epoxy Compounds: Organic compounds that include a cyclic ether with three ring atoms in their structure. They are commonly used as precursors for POLYMERS such as EPOXY RESINS.Diazonium CompoundsCladosporium: A mitosporic Loculoascomycetes fungal genus including some economically important plant parasites. Teleomorphs include Mycosphaerella and Venturia.Aspergillus: A genus of mitosporic fungi containing about 100 species and eleven different teleomorphs in the family Trichocomaceae.Azo CompoundsXylariales: An order of ascomycetous FUNGI which includes many economically important plant parasites as well as saprophytes.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Mutagenesis, Site-Directed: Genetically engineered MUTAGENESIS at a specific site in the DNA molecule that introduces a base substitution, or an insertion or deletion.Kinetics: The rate dynamics in chemical or physical systems.Molecular Weight: The sum of the weight of all the atoms in a molecule.