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1,3-β-Glucanase I is one of the three 1,3-β-glucanase enzymes which are developmentally regulated in Penicillium italicum. On incubation of the fungus in derepressing medium (limited in glucose), 1,3-β-glucanases II and III are produced first, followed by 1,3-β-glucanase I. We have purified the latter enzyme 290-fold from cell-free extracts of derepressed mycelium. The purification involved Sephadex G-100 chromatography, adsorption to DEAE-Sephadex, concanavalin A-Sepharose and preparative isoelectric focusing. The purified enzyme appeared homogeneous on SDS-PAGE. The apparent molecular weights estimated by Sephadex G-100 filtration and SDS-PAGE were 65000 and 68000 respectively. The enzyme appears to be an acidic glycoprotein (pI 4·7) with an endo-splitting mode of action, clearly different from 1,3-β-glucanases II and III. The K m on a standard, slightly branched 1,3-β-glucan (laminarin) was 0·04 mg ml-1, at least ten times lower than the average Km for β-glucanases. It showed almost no activity on heavily branched substrates (yeast wall glucan). An evaluation of the physicochemical properties and other characteristics suggests a metabolic role for this endo-1,3-β-glucanase.
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