By Martyn Herman

LONDON (Reuters) - Kell Brook admits to feeling fear but says he is ready to inflict a first career defeat on Kazakh knockout specialist Gennady Golovkin when they meet in a London ring on Saturday.

Golovkin, who boasts a perfect 35-0 record with 32 KOs, puts his WBC and IBF middleweight belts on the line against unbeaten IBF welterweight champion Brook who has moved up two weight divisions for the biggest fight of his career.

Amiable as a dapper Golovkin appeared at a news conference on Thursday, describing his love for London and its people, he has proved a ruthless beast inside the ropes and is regarded as the best pound-for-pound boxer in the world, dominating the middleweight ranks.

"There is fear for me in this fight, but that will make me so sharp," Briton Brook, who recovered from a life-threatening stabbing while on holiday in Spain two years ago, told reporters across the Thames from the O2 Arena that will stage the contest.

"That fear is healthy because I need to be switched on throughout the fight. This is my moment. I'm going in there to win. Very confident. I'm going to shock the world."

Golovkin's trainer Abel Sanchez warned Brook that he was in for a rude awakening on Saturday, questioning the wisdom of moving up to middleweight for the first time.

"It takes more than a 10-week scientific experiment to topple Gennady Golovkin," he said.

Golovkin's WBA belt is not up for grabs as that ruling body refused to sanction the fight, saying it was concerned about Brook's safety in the 160lbs division.

However, Brook says it is a natural step and that he will finally be able to fight at 100 percent.

"When I've had to take weight off to make 147 (lbs) it's meant I fight at 60 or 70 percent," Sheffield's Brook, who owns a 36-0 record, said.

"You are going to see the full 100 percent."

Brook's trainer Dominic Ingle also played down concerns that his charge was moving out of his depth.

"We used to have to take muscle off him (to make the weight)," he said. "This is not a big guy versus a small guy. This is two middleweights. We've left no stone unturned to prepare for the fight.

"No one is giving Kell a chance. But he is coming to win."

Golovkin is eyeing a 17th consecutive middleweight title victory. Many had hoped he would fight Mexican Saul Alvarez but their proposed showdown fell through.

His promoter Tom Loeffler said finding opponents willing to climb into the ring with Golovkin was difficult, which is why Brook's challenge has stoked such interest and meant 17,000 tickets sold in nine minutes, according to promoters Matchroom.

"Brook is a champion, undefeated. He's not scared," Golovkin said. "Respect. He's a fighter."

(Reporting by Martyn Herman; editing by Clare Lovell)