Showing papers on "Chitin published in 1971"

The Control of Morphogenesis: An Enzymatic Mechanism for the Initiation of Septum Formation in Yeast

Abstract: Previous work with yeast has indicated that chitin is the specific component of the septum between mother and daughter cell. Experiments with synchronized cells show that chitin synthesis is initiated at a precise time in the cell cycle. Newly discovered features of the chitin synthetase system suggest how this specificity in location and timing can be achieved. The particulate chitin synthetase is shown to exist almost entirely in an inactive or zymogen state. The zymogen can be converted into an active form either by an enzyme (activating factor) present in yeast or by trypsin. The activating factor is found in a particulate fraction, but can be solubilized by mild sonic oscillation. A heat-stable protein, previously isolated from yeast and believed to inhibit chitin synthetase, has now been found to act as an inhibitor of the activating factor to which it binds very tightly. It is proposed that chitin synthetase, in the zymogen form, is uniformly distributed on the cytoplasmic membrane. At the time of septum initiation, vesicles carrying the activating factor would be directed to specific sites and bring about the localized conversion of the zymogen into the active form. A molecular model is thus introduced for processes of morphological change and differentiation.

Monosaccharide and Chitin Content of Cell Walls of Histoplasma capsulatum and Blastomyces dermatitidis

Abstract: Cell walls of Histoplasma capsulatum and Blastomyces dermatitidis, obtained by mechanical breakage of yeast- and mycelial-phase cultures, were lipid-extracted and then fractionated with ethylenediamine. Unextracted cell walls, lipid-extracted cell walls, and the three fractions resulting from ethylenediamine treatment were examined for monosaccharide and chitin content. The yeast-phase cell walls of five strains of H. capsulatum fell into two categories, designated chemotypes I and II, one of which, chemotype II, was similar to yeast-phase cell walls derived from three strains of B. dermatitidis. H. capsulatum chemotype I cell walls were characterized by lower content of material soluble in ethylenediamine, higher chitin content, and lower monosaccharide content than H. capsulatum chemotype II or B. dermatitidis cell walls. Approximately 80% of the monosaccharides of chemotype I cell walls was combined in forms susceptible to attack by mild acid hydrolysis, compared with about 50% of the monosaccharides of chemotype II and B. dermatitidis. H. capsulatum and B. dermatitidis yeast-phase cell walls could be distinguished, however, by their susceptibility to attack by a crude enzyme system derived from a Streptomyces sp. incubated with chitin as the only carbon source. Both glucose and acetylglucosamine were released from H. capsulatum cell walls, regardless of chemotype, during enzymatic hydrolysis, whereas only acetylglucosamine was released from B. dermatitidis yeast-phase cell walls. Mycelial-phase cell walls of H. capsulatum and B. dermatitidis were characterized by lower content of material soluble in ethylenediamine, higher proportions of mannose, and lower chitin content than their respective yeast phases. Glucose and acetylglucosamine were both released from all mycelial-phase cell walls, whether H. capsulatum or B. dermatitidis, by the crude enzyme system.

Enzyme Regulation, Lysine Pathways and Cell Wall Structures as Indicators of Major Lines of Evolution in Fungi

Abstract: The distribution of the two known pathways of lysine biosynthesis can be correlated with allosteric controls of enzymes and dichotomy of cellulose and chitin in fungi.

Chitin and chitin derivatives for promoting wound healing

Abstract: Wound healing compositions and the process of healing wounds with such compositions are described, the compositions containing chitin, partially depolymerized chitin or a chitin derivative.

Changes in the rate of chitin synthesis during the crayfish molting cycle

Abstract: 1. 1. The amount of 14 C glucose incorporated into the chitin of crayfish served as an indication of the rate of chitin synthesis. 2. 2. It was found that chitin synthesis occurred at all stages of the molting cycle, including C 4 (the intermolt). 3. 3. There was a significant increase in the rate of incorporation during premolt stage D 2 , and the amount of chitin synthesis continued to increase at each successive stage until after the molt, when it reached a peak at stage B.

Lysis of an Aspergillus nidulans mutant blocked in chitin synthesis and its relation to wall assembly and wall metabolism

Abstract: 1. Mutant Aspergillus nidulans hyphae containing 7–15% of the normal chitin complement did not lyse in dilute buffer but lysed on continued incubation in growth medium without osmotic stabiliser. Distortion and lysis could occur anywhere along the hypha and were not confined to the apex. 2. Hyphae with a normal chitin content started to distort and lyse 90 min after transfer to medium lacking osmotic stabiliser and at the temperature inhibiting chitin synthesis. Lysis was not confined to the growing tips. 3. Hyphae lacking wall chitin and transferred to conditions where chitin synthesis could proceed, formed stable mycelium at the growing tips and distorted in the older, chitin-poor, regions. Pulse-labelling with N-acetylglucosamine and radioautography showed that, in such hyphae, chitin was incorporated into the wall in the older regions undergoing distortion. 4. The relation between growth—dependent distortion and lysis and the activity and location of autolytic enzymes is discussed.

The composition of peptidochitodextrins from sarcophagid puparial cases

Abstract: 1. N-Bromosuccinimide cleaved proteins and pigments from fly puparia, increasing the chitin:protein ratio from 0.5 to 1.5. The product afforded subfractions (ratio 5:1) of molecular weights of 1200 and 1600 devoid of aromatic residues and N-terminal β-alanine, direct aryl links between polysaccharide chains being discounted. 2. The chitin–protein complex decreased in molecular weight when treated with Pronase, which suggested polypeptide bridges within the native chitin micelle. The limit dextrins generated by chitinase were mixtures of unsubstituted dextrins and peptidylated oligosaccharides, with the former predominating. 3. Peptidochitodextrins of similar molecular weight but markedly different solubility were prepared, which were indistinguishable with respect to amino acid, glucosamine, acetyl, X-ray or infrared characteristics. It is suggested that physical interactions contribute to the stability of the integument in addition to the covalent bonds that form during sclerotization.

Blood sugar metabolism during moulting in the isopod crustacean Ligia exotica

Abstract: Blood sugar metabolism of the isopod Ligia exotica Roux was studied in relation to chitin synthesis during the moult cycle. The blood sugars were found to occur free, as well as bound with blood proteins, during all moult stages, as in Emerita asiatica. The variety of free blood sugars is smaller in L. exotica; it comprises only glucose and glucose-6-phosphate. The protein-bound blood sugars are glucose and glucosamine. The blood-volume values do not differ markedly during the moult cycle. Estimations of blood sugars showed a marked rise of sugar levels in the blood during the premoult phase, and a subsequent fall during the freshmoult phase, when chitin is actively synthesised. The chitin values also showed a definite correlation with the blood-sugar values. The increased resorption of chitin during the premoult stage, and its liberation into the blood stream as glucosamine, is indicative of its reutilisation in chitin synthesis as in E. asiatica and the genus Cecropia. As more immediate precursors of chitin, such as uridine diphosphate and uridine diphophate acetylglucosamine compounds, were absent in the blood, a thorough biochemical study of the epidermis is suggested to locate the intermediate precursors of chitin which are possibly derived from blood sugars.