N-linked protein glycosylation in the rat parotid gland during aging.
N-Linked protein glycosylation was examined in vitro in dispersed rat parotid acinar cells from young adult (3-6 months) and aged (22-24 months) rats. A small decrease in general protein production was observed with cells from aged animals (approximately 20% lower incorporation of [14C]leucine into 10% CCl3 COOH insoluble protein during continuous pulse labeling). Incorporation of [3H]mannose into N-linked glycoproteins by aged cells was further reduced (approximately 35%). Similarly microsomal membranes from parotid glands of aged animals showed approximately 50% reduction in the synthesis of mannosylphosphoryl dolichol, a key intermediate in the dolichol pathway of protein N-glycosylation. Man-P-Dol synthase, the microsomal enzyme responsible for production of this saccharide-lipid, displayed no change in apparent Km for GDP-mannose when preparations from aged animals were utilized, but did show approximately 50% reduction in Vmax. Following beta-adrenoreceptor activation, cells from both young adult and aged glands showed increased N-linked protein glycosylation almost to the same extent (approximately 2-fold). The data suggested that in aged rat parotid cells there is a basal reduction of activity in the pathway responsible for asparagine-linked protein glycosylation, but that following exocytotic stimuli this pathway responds in a manner comparable to cells from young adult glands.
Kousvelari
E E
EE
Clinical Investigations and Patient Care Branch, National Institute of Dental Research, Bethesda, MD 20892.
Banerjee
D K
DK
Murty
L
L
Baum
B J
BJ
D000375:Aging / Q000378:metabolism*; D000818:Animals; D006031:Glycosylation; D007700:Kinetics; D008297:Male; D008364:Mannosyltransferases / Q000032:analysis; D010306:Parotid Gland / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000502:physiology
D011506:Proteins; D011943:Receptors, Adrenergic, beta; D008364:Mannosyltransferases; C022755:dolichyl-phosphate beta-D-mannosyltransferase