Lewis Stevens

Egg white proteins

1. Egg white proteins are the principal solutes present in egg white, making up approximately 10% of its weight. 2. They are globular proteins and most have acidic isoelectric points. 3. Many are glycoproteins with carbohydrate contents ranging from 2 to 58%. 4. Of the major egg white proteins, lysozyme is the only one having catalytic activity, but many have specific binding sites, e.g. for vitamins such as biotin, riboflavin and thiamin, or for metal ions such as FeIII. 5. A major group are those showing proteinase inhibitory activity, and they include ovomucoid, ovoinhibitor, cystatin and ovostatin. 6. The synthesis of egg white protein occurs in the oviduct, and is hormonally controlled either by oestrogens or progesterone. 7. Extensive studies have been carried out in the genes coding for egg white proteins.

Spermine, Spermidine and Putrescine in Fungal Development

Publisher Summary A number of different naturally-occurring oligoamines exist but only three are known to be widely distributed—namely, putrescine (1,4-diaminobutane), spermidine (4 azaoctane- 1,8-diamine), and spermine (4,9 diazadodecane-l,12-diamine). Because there is a correlation among oligoamine synthesis, cell growth, and differentiation and as the latter process cannot be easily studied in bacteria, fungi have a number of advantages in studying differentiation. Fungi exhibit a wide variety of developmental patterns many of which can be varied under laboratory conditions. Also, extensive genetic analysis can often be carried out on fungi. They are suitable phyllum for studying the role of oligoamines in development, and this helps to solve the more general question of oligoamine function. The chapter discusses the distribution and biosynthesis of oligoamines with particular emphasis on the contrast between prokaryotes and eukaryotes. Oligoamine distribution and synthesis in fungi, and related amino-acid biosynthesis is presented. Fungal development, with emphasis on correlations among nucleic acid, protein, and oligoamine synthesis, is also discussed.

The biology and chemistry of polyamines : Edited by S.H. Goldemberg and I.D. Algranati; Oxford University Press; Oxford, 1990; xiii + 244 pages; £30.00

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The effects of 1,4-diaminobutanone on polyamine synthesis in Aspergillus nidulans

The naturally occurring polyamines, putrescine, spermidine and spermine are synthesized in most eucaryotes from ornithine and methionine [ 1,2] by the pathway outlined in fig. 1. The functions of these amines which often occur in millimolar concentrations [ 1,2] are unknown. They are synthesized most rapidly in proliferating cells [2]. In order to try to establish their functions much work has recently focussed on the development of specific inhibitors of polyamine synthesis [3-l 11. Putrescine occupies a central position in the synthesis of spermidine and spermine: (i) It has been found to inhibit the production of ornithine decarboxylase [12-l 71 (ii) It is a weak competitive inhibitor of ornithine decarboxylase [ 17-20 J (iii) It is an activator of S-adenosyl methionine decarboxylase [ 17,20-231 (iv) It is a substrate for spermidine synthase [ 1,2] (v) It is a competitive inhibitor of spermine synthase [241. During a search for a gratuitous repressor of ornithine decarboxylase such as has now been found for this enzyme in regenerating liver [25] we tested a number of compounds having structures similar to putrescine and found that one of these, 1:4 diaminobutanone, stimulated the increased production of ornithine decarboxylase in germinating conidia of Aspergillus nidulans. On further examination this compound was found to be a powerful competitive inhibitor of ornithine decarboxylase, it could replace putrescine as an activator of S-adenosyl methionine decarboxylase, and it also caused a reduction in the intracellular concentrations of spermidine and spermine.

Purification and Properties of Two Neutral Proteinases from Aspergillus nidulans

Two proteinases have been purified from mycelial extracts of Aspergillus nidulans. Both enzymes have pH optima between 6.5 and 7.5 and are inhibited by phenylmethane sulphonyl fluoride and by di-isopropyl fluorophosphate. The molecular weights and isoelectric points of proteinase I and proteinase II are 30 900 and 30 000, and 4.6 and 4.3, respectively. Both enzymes have a similar range of substrate specificities. The principal differences in their properties are that proteinase I is sensitive to inhibition by 1 mM mercurials whereas proteinase II is not appreciably inhibited at this concentration, and that proteinase I is much more sensitive to denaturation by urea, guanidine hydrochloride and sodium dodecyl sulphate.

Ornithine decarboxylase activity in germinating conidia of Aspergillus nidulans.

The cellular functions of the naturally occurring polyamines, putrescine, spermidine and spermine are unknown. Several workers [1-4] have used putrescine auxotrophs ofE. coli in order to try to establish which cell processes are impaired when the intracellular concentration of polyamines are reduced. A mutant of Aspergillus nidulans was reported by Sneath [5] in 1955 to have an absolute requirement for putrescine for growth. However, the observations described in this paper using a recombinant of Sneaths original auxotroph show that putrescine is required for germination of the conidia but not for subsequent hyphal growth. This transient putrescine requirement during germination of the mutant is due to a deficiency in ornithine decarboxylase at a time when there is a rapid increase in omithine decarboxylase in a similar prototroph of Aspergillus nidulans. The increase in ornithine decarboxylase activity in the prototroph corresponds with the period of most rapid RNA synthesis.

A comparative study of the structure of egg-white riboflavin binding protein from the domestic fowl and Japanese quail

1. The riboflavin binding proteins from domestic fowl and Japanese quail have been isolated and their structures compared by circular dichroism, fluorescence and peptide mapping. 2. The two proteins have similar secondary structures, but differ in their tertiary structures as reflected in the environments of aromatic amino acid side chains. 3. Differences in amino acid sequence between the proteins are indicated by the digestion patterns obtained with thermolysin, chymotrypsin and V8 proteinase from Staphylococcus aureus. Both proteins are resistant to digestion by trypsin.

Unfolding and refolding of hen egg-white riboflavin binding protein

The unfolding and refolding of riboflavin-binding protein (RfBP) from hen egg-white induced by addition of guanidinium chloride (GdnHCl), and its subsequent removal by dialysis have been studied by c.d. and fluorescence for both the native and reduced protein. The reduction of its nine disulphide bonds causes a reduction in the secondary structure (alpha-helix plus beta-sheet) from 63% to 33% of the amino acid residues. Unfolding of the native protein occurred in two phases; the first involving a substantial loss of tertiary structure, followed by a second phase involving loss of secondary structure at higher GdnHCl concentrations. By contrast this biphasic behaviour was not discernible in the reduced protein. The loss of ability to bind riboflavin occurred after the first phase of unfolding. Comparison of unfolding of the holoprotein and apoprotein suggested that riboflavin has only a small stabilizing effect on the unfolding process. After removal of GdnHCl, the holoprotein, apoprotein and reduced protein assumed their original conformation. The significance of the results in relation to various models for protein folding is discussed.

Polyamine stimulation of in vivo rates of macromolecular synthesis in a putrescine auxotroph of Aspergillus nidulans

(NH*-(CH&-NH& spermidine (NH&CH&- NH-(CH&-NH2) and spermine (NH,-(CH&- NH-(CHz)4-NH-(CH&-NH2) are ubiquitous cations whose precise physiological roles remain unclear. It has been proposed that polyamines are involved in the synthesis of nucleic acids and proteins and/or maintaining membrane stability [ 11. Investiga- tions of E. coli polyamine auxotrophs have demon- strated a role for polyamines in protein synthesis that is independent of transcription [2,3]

Detection of a Proteinase Inhibitor in Aspergillus nidulans

The activity of proteinases in mycelial extracts of Aspergillus nidulans increased during storage. The rate of activation increased with temperature. Three separate proteinase activities, differing in their electrophoretic mobilities on polyacrylamide gels, were readily detected at pH 6.5. Inhibitory activity, effective against all three proteinase activities, was also detected in fractions prepared from fresh mycelial extracts. The inhibitory factor(s) were heat-stable and non-dialysable. The inhibitory activity was lost during storage of mycelial extracts. It is proposed that the inhibitory factor(s) are digested by the proteinases during storage.