Zinc coordination, function, and structure of zinc enzymes and other proteins

On the average hydrophobicity of proteins and the relation between it and protein structure.

The aminopeptidase from hog intestinal brush border

Starch-degrading, amylolytic enzymes are widely distributed among microbes. Several activities are required to hydrolyze starch to its glucose units. These enzymes include alpha-amylase, beta-amylase, glucoamylase, alpha-glucosidase, pullulan-degrading enzymes, exoacting enzymes yielding alpha-type endproducts, and cyclodextrin glycosyltransferase. Properties of these enzymes vary and are somewhat linked to the environmental circumstances of the producing organisms. Features of the enzymes, their action patterns, physicochemical properties, occurrence, genetics, and results obtained from cloning of the genes are described. Among all the amylolytic enzymes, the genetics of alpha-amylase in Bacillus subtilis are best known. Alpha-Amylase production in B. subtilis is regulated by several genetic elements, many of which have synergistic effects. Genes encoding enzymes from all the amylolytic enzyme groups dealt with here have been cloned, and the sequences have been found to contain some highly conserved regions thought to be essential for their action and/or structure. Glucoamylase appears usually in several forms, which seem to be the results of a variety of mechanisms, including heterogeneous glycosylation, limited proteolysis, multiple modes of mRNA splicing, and the presence of several structural genes.

Microbial amylolytic enzymes

Calcium is involved in many biological functions and in most types of cell motility. Among the best-investigated calcium-dependent processes are excitation-contraction coupling in muscle, glycogen metabolism, membrane permeability, transmission of nerve impulses, release of neurotransmitters, cytoplasmic streaming, cell division, and secretory mechanisms. Disturbance of calcium homeostasis can lead, for example, to defective bone mineralization (osteomalacia and rickets), renal failure, malignant hyperthermia, and parturient paresis in ruminants, and may have a pathophysiological role in the progression of muscular dystrophy. Cancer cells have been found to have abnormally large levels of calcium-binding proteins. It is thought that this may lead to a permanent activation of DNA synthesis without an extracellular calcium surge serving as a trigger. In this context it is of interest that a tumor-specific, CaZ+-binding protein, oncomodulin, not present in normal fetal and adult tissues, has been discovered in rat hepatomas and other tumor cells 6~. The mechanism of action of calcium is different from that of other metal ions but similar to the regulatory action of cyclic nucleotides. They initiate multiple metabolic effects by binding to the regulatory subunit of cyclic AMP-dependent protein kinases which in turn modulate a number of additional enzyme activities. By analogy to the cyclic AMP system, it has been proposed that calcium represents another intracellular 'second messenger '75. Binding to various calcium binding proteins such as parvalbumin, calmodulin, S-100-proteins, vitamin D-dependent calcium-binding proteins and troponin-C (the calcium binding subunit of troponin), resuits in an amplification of the calcium signal and in analogy to the cyclic AMP signal, initiates a number of calcium-dependent mechanisms. Parvalbumin, together with these proteins belongs to a homologous family of CaZ§ receptors 54. This is based on amino acid sequence data combined with a crystal structure analysis of carp parvalbumin (pI = 4.25). Although these proteins are structurally related, owing to their common evolutionary origin 37, their cellular and intracellular distributions are quite different, indicating different physiological functions. Calmodulin has been found to be involved in a variety of qellular activities 63 and troponin-C, the Ca2+-binding subunit of troponin, is responsible for the calcium sensitivity of muscle contraction 26. Vitamin D-dependent calcium-binding proteins are possibly required for calcium transport or to act as an intracellular calcium buffer system 8~ S-100 proteins 5~ are a family of acidic proteins primarily found in glial cells of the brain but recently iological function is still unknown. A class of calcium-binding proteins containing the modified amino acid, 7-carboxyglutamic acid 32 are involved in blood coagulation and bone formation. Their synthesis requires vitamin K, hence these proteins have been termed the vitamin K-dependent proteins. Parvalbumins are small water-soluble proteins originally believed to be present only in skeletal muscles of lower vertebrates and which seemed to disappear in the course of evolution with the transition to terrestrial life. Previous reviews about parvatbumin have focussed mainly on the structural aspects of this protein in the muscles of lower vertebrates 23' 54, 82. Although considerable information has been gathered in the past concerning the primary and secondary structures as well as calcium-binding properties of muscle parvalbumin from fish and amphibia, only limited evidence for its biological significance could be obtained. This review will summarize the biochemical properties of parvalbumins from mammalian muscle and nonmuscle cells, describe its cellular distribution and try to explore its physiological function. It will be shown that parvalbumin is always present in distinct populations of cells in some tissues where it is most probably involved in more specialized CaZ+-dependeut physiological processes. Quite in contrast, calmodulin is found in all eukaryotic cells, and has multiple regulatory functions in them.

Parvalbumin, and intracellular calcium-binding protein; distribution, properties and possible roles in mammalian cells

Isolation and characterization of parvalbumins from the skeletal muscle of higher vertebrates.

THE RESISTANCE OF α-AMYLASES TOWARDS PROTEOLYTIC ATTACK

The Amino Acid Composition of α-Amylase from Bacillus subtilis

Bacillus subtilis α-amylase, a zinc-protein complex

Pig kidney particulate aminopeptidase (EC 3.4.1.2) was purified by a modification of the procedure of Wachsmuth et al. [3] to a state of homogeneity according to criteria of ultracentrifugation and polyacrylamide gel electrophoresis, and some of its physical and chemical properties were determined.



The purified enzyme (specific activity 30 ± 3 μmoles leucine-p-nitroanilide hydrolyzed/min/mg) has a s20,w = 9.82 S at pH 8 and a molecular weight of about 280,000 as determined by high speed sedimentation equilibrium. Divergence between the number-, weight- and z- average molecular weights, and a sharp decrease of these values at low protein concentration, suggest that one is dealing with an associating-dissociating system.



Amino acid analysis revealed the presence of considerable quantities of carbohydrates in the enzyme. Colorimetric, gas chromatographic and enzymatic analyses demonstrated the presence of glucosamine, galactose, mannose, fucose and sialic acid residues in the ratio of 1:0.89:0.75: 0.13: 0.13, amounting to ca. 400 residues or 20% (56,000 daltons) of the molecular weight. With the exception of sialic acid, the carbohydrate content was remarkably constant from preparation to preparation.



Analyses by both atomic absorption spectrometry and the dithizone method showed that zinc–the only metal found in significant amount–was always present in the ratio of 2 atoms per molecule. It is therefore proposed that pig kidney particulate aminopeptidase is a Zn-containing glycoportein.

Physical and chemical characterization of pig kidney particulate aminopeptidase.

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