ISSN:
0739-4462
Keywords:
proteolytic processing
;
yolk enzymes
;
Chemistry
;
Food Science, Agricultural, Medicinal and Pharmaceutical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
Notes:
Various aspects of the processing of Blattella germanica vitellin (Vt) in the oocyte and egg have been investigated. Employing subunit specific antibodies, the precursor product relationships among the subunits of this Vt have been determined. After endocytosis of Vt by the oocyte, the Mr 160,000 subunit Vt is cleaved to products of Mr 95,000 and Mr 50,000. In association with an unprocessed Mr 102,000 peptide, these form the subunits of the Vt of freshly ovulated eggs. Between 4 and 5 days post ovulation (at 30°C), all three subunits of Vt are again processed proteolytically before use by the embryo. Although Vt's high mannose-type oligosaccharides are trimmed during embryogenesis, their modification occurs subsequent to the day 4-5 proteolysis, precluding the possibility that changes in oligosaccharide content or structure contribute to regulating this second proteolytic event. Although the predominant oligosaccharide of Vt is Man9GlCNAc2, the Mr 50,000 subunit of egg-borne Vt contains a much higher proportion of Man6GlCNAc2 than the other two subunits; therefore, this portion of the precursor vitellogenin must be more accessible to the processing mannosidases of the endoplasmic reticulum during its biosynthesis. A microtechnique for aspirating the yolk from individual eggs in an oothecapermits its isolation free of contamination by embryonic tissue. With this procedure, the specific activity profiles of exo-α-mannosidase, exp-β-N-acetylglucosaminidase, α-glucosidase and acid phosphatase were monitored during the first 6 days after ovulation, and some of their properties were also determined. Expression of the acid phosphatase and exo-β-N-acetyl-glucosaminidase activities coincide with the day 4-5 proteolysis, while α-mannosidase remains relatively constant throughout the first 6 days. Functions for these enzymes and the oligosaccharides of Vt during Vt storage and utilization are proposed.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/arch.940080105
