Extensin Secreted into the Culture Medium by Tobacco Cells I. Purification and Some Properties

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Abstract
The medium of 12-day-old culturs of tobacco cells (Nicotiana tabacum L., var Xanthi; line XD-6S) contain c.a. 160mg/liter of protein, of which 14% of the constituent ami no acids were found to be hydroxyproline. By sequential column chromatographies and CsCl density-gradient centrifugation, a basic hydroxyproline-rich glycoprotein was purified from the medium and found to have an amino acid composition typical of extensin; with a high level of hydroxyproline (33mole%), tyrosine (13%), and lysine (14%). The glycoprotein contained 42% (w/w) of sugars, among which arabinose was the major component (85%). The proportion of this extensin in the proteins in the culture medium was estimated to be much higher than that of arabino-galactan protein (about 5 times higher) on a protein basis, with extensin comprising between 25% and 41%, and probably about 37% of the proteins in the medium.