UPDATE 1-Verbund converts bond to Sorgenia shares -CIR CEO

* Verbund holds 44.77 pct Sorgenia, CIR has 51.85 pct

* Deal comes amid speculation of Spanish interest

* CIR says deal proof of Verbund's commitment to Sorgenia

(Adds details, background, share price)

MILAN, June 17 (Reuters) - Austria's top utility Verbund (VERB.VI) has converted a 150 million euro ($208 million) bond into shares in Italian industrial holding CIR's (CIRX.MI) energy unit Sorgenia, CIR said on Wednesday.

The deal, announced ahead of the August deadline for conversion, does not change the control structure of the Sorgenia group. CIR holds 51.85 percent of Sorgenia, Italy's biggest privately held energy group, and Verbund 44.77 percent, CIR said in a statement.

"The two capital increases made in the last year are proof of the commitment of our historical partner Verbund to join CIR in the important investment plan of Sorgenia," CIR Chief Executive Rodolfo De Benedetti said.

Sorgenia, CIR's biggest single asset, had revenues of 2.43 billion euros in 2008. The deal values the unit at 3.9 billion euros.

Bestinver Gestion, a fund management company owned by Spanish builder Acciona (ANA.MC), has built stakes in CIR and its parent Cofide (COFI.MI) amid speculation Acciona could be looking to expand its renewable energy business in Italy.

Bestinver has said its CIR investments are financial.

CIR completed a first 200 million euro capital increase in June 2008.

At 1015 GMT CIR shares were down 5 percent at 1.039 euros, more than twice the downturn in the DJ Stoxx utilities index .SX6P (Reporting by Stephen Jewkes, editing by Will Waterman) ($1=.7200 Euro)